This was CNBC's live blog tracking developments on the war in Ukraine. See here for the latest updates.

Ukrainian President Volodymyr Zelenskyy concluded a meeting with U.S. senators Tuesday morning in Washington, after which Senate Majority Whip Dick Durbin said he was "angry that we would consider walking away from Ukraine at this moment" in history.

"What does it mean in the future when the United States says, 'We're on your side?' Does it mean anything if we walk away from Ukraine? I don't think so," Durbin told reporters, according to NBC News.

Zelenskyy is taking part in a series of meetings with officials ahead of talks and a press conference with President Joe Biden later Tuesday, as concerns grow over the U.S.' commitment to donate more aid to Kyiv.

Continued funding for Ukraine is a bone of contention among U.S. lawmakers, although Biden and Ukraine's other allies have warned that a cessation in aid could lead to a victory for Moscow. Republican U.S. Senator J.D. Vance said Sunday that Ukraine may need to cede some land to Russia in order to end the war.

The meeting also comes as another top Ukrainian security official admitted that Ukraine's counteroffensive had not lived up to hopes and expectations.

Ukraine deputy PM: Confident there are enough options to reach an EU aid deal

Ukrainian Deputy Prime Minister Olga Stefanishyna told CNBC's Silvia Amaro Tuesday she believes that there are enough options on the table for the European Union to pass a 50 billion euro ($54 billion) aid facility for Kyiv at its summit on Dec 14-15.

The agreement will be closely tied to discussions over whether to begin formal talks over Ukraine's accession to the bloc, she said.

"Following my conversations I had here in Brussels, I am confident that at this particular point there are enough options on the table for a discussion with leaders which would allow to balance the interests of all parties, answer partially the questions and concerns raised by the Hungarian government," Stefanishyna said.

Hungarian Prime Minister Viktor Orban has threatened to veto the aid package, which is supported by all the bloc's other member states. Hungary may also obstruct the start of accession talks.

Orban has retained cordial ties with Russian President Vladimir Putin during the war, recently meeting with him at China's Belt and Road Summit. Meanwhile, Hungary has seen escalating tensions with Ukraine over issues such as cross-border exports. Hungarian officials have frequently criticized EU policy on the war, arguing that isolating Russia and arming Ukraine was not the right approach.

The funding approval is particularly vital to Ukraine as it coincides with uncertainty over the future of funding from the U.S., its biggest donor, along with the onset of winter, fierce frontline fighting and increased Russian attacks on civilian infrastructure.

"The busy job [negotiating] between the member states has brought us to understanding there are pretty many options on the table which makes me feel more positive that there is a way to find a solution and avoid failure to take any decision over the next days," Stefanishyna said.

Ukraine understands the European Commission has safeguarding options that would secure financial support for 2024 at least, "but of course absence of this decision would lead to total uncertainty in terms of ability to ensure the sustainability of Ukraine's budget," she said.

It is also "not a very good signal to other partners, including those across Atlantic, that the EU is not able to form a strategic vision of supporting Ukraine throughout the complicated circumstances of war," she added.

— Jenni Reid

Ukraine mobile operator says IT infrastructure 'partially destroyed' by cyberattack

The chief executive of Ukraine's largest mobile operator, Kyivstar, says the company's IT infrastructure has been "partially destroyed" by a cyberattack earlier Tuesday.

CEO Oleksandr Komarov said on national television that the attack had "significantly damaged the [IT] infrastructure, limited access, we could not counter it at the virtual level, so we shut down Kyivstar physically to limit the enemy's access," according to comments translated by Reuters.

Kyivstar said earlier that it had been "the target of a powerful cyber attack" that had left mobile connections and internet access temporarily unavailable. It said law enforcement bodies were investigating "the circumstances and consequences of illegal interference in the activity of the network."

It did not provide any detail on who it believed was behind the cyberattack but stated, "yes, our enemies are insidious. But we are ready to face any difficulties, overcome them and continue working for Ukrainians."

— Holly Ellyatt

Poland's Tusk says he will push for West's full commitment to Ukraine

Poland's newly appointed prime minister, Donald Tusk, said on Tuesday his country will demand the full mobilization of the West to help Ukraine, adding it will regain a leadership position in Europe and will be a strong part of NATO.

Poland's parliament backed Tusk to become prime minister on Monday, ending eight years of nationalist rule and putting the country on track for a thawing of relations with the European Union.

Tusk, a former European Council president, will face a vote of confidence later on Tuesday.

"We will ... loudly and decisively demand the full mobilization of the free world, the Western world, to help Ukraine in this war," Tusk said in parliament, presenting his government's plans.

Ukrainian President Volodymyr Zelenskyy is due to hold talks with U.S. leaders on Tuesday, making his case for more U.S. aid for Ukraine's war against Russia at a time of increasing doubts among many Republican lawmakers.

Tusk added Poland's eastern border would be secure and vowed to quickly solve issues related to a truckers' protest on several border crossings with Ukraine.

— Reuters

Russian links with China, Iran and North Korea a threat, warns Finland

Russia's increasing cooperation with China, Iran, North Korea and its other global allies is a serious, long-term threat to European countries, Finland's Defence Minister Antti Hakkanen said on Tuesday.

Finland and Estonia are investigating the destruction in October of the Balticconnector gas pipeline and telecom cables on the Baltic seabed and have named a Hong Kong registered container vessel as their main suspect for the damage.

"While these issues are not public, what Russia does at the moment together with China, Iran, North Korea and its other allies, also from the global south, constitutes a very serious prospect in the long term," Hakkanen said in a speech.

As the NATO military alliance's newest member, which shares a 1,340-km (830-mile) border with Russia, Finland and its intelligence services are monitoring Russia's action globally, Hakkanen said.

He called Russia's new cooperation with its global allies "a weather system of security policy that is unfortunately troublesome."

— Reuters

Ukrainian biggest mobile operator hit with 'powerful' cyberattack

Ukraine's biggest mobile operator, Kyivstar, said it was hit by a "powerful" cyberattack on Tuesday, stating the attack was the result of "illegal interference."

"This morning we were the target of a powerful cyber attack," the company said in a statement on Facebook.

The attack caused a technical failure that means mobile connections and internet access are temporarily unavailable, it said.

"Of course, this is a challenge for us," it added, noting that law enforcement bodies were investigating "the circumstances and consequences of illegal interference in the activity of the network."

Kyivstar did not provide any detail on who it thought could have carried out the cyberattack but stated, "yes, our enemies are insidious. But we are ready to face any difficulties, overcome them and continue working for Ukrainians."

Kyivstar said that the personal data of customers had not been compromised at the current time and that it was working to restore the network.

"We are working on eliminating the consequences for the fastest possible restoration of communication," it added.

— Holly Ellyatt

Kremlin says it's closely monitoring Biden-Zelenskyy meeting

The Kremlin said Tuesday that it will be closely monitoring the upcoming meeting meeting between U.S. President Joe Biden and Ukraine's leader Volodymyr Zelenskyy.

Speaking to reporters, Kremlin Press Secretary Dmitry Peskov said the meeting, in which Biden and Zelenskyy are expected to discuss the prospect of a large chunk of additional funding for Ukraine, would not change the course of what Russia calls its "special military operation."

"It is important to understand that tens of billions of dollars pumped into Ukraine did not help it gain any success on the field battle. Other tens of billions will be doomed to the same fiasco," Peskov said, according to comments published by Tass.

Peskov said the meeting would be monitored "very carefully" nonetheless.

Russia is certainly hoping that additional aid for Ukraine is blocked as it hopes to outlast Ukraine and its allies' ability to continue fighting as the war approaches its second anniversary. Intense negotiations are ongoing on Capitol Hill as the White House tries to get Republican lawmakers to back a $106 billion supplemental package of wartime funding for Ukraine, as well as Israel, and domestic border security.

— Holly Ellyatt

Russia considers any intervention over 'missing' Putin critic Navalny 'unacceptable'

The Kremlin is being tight-lipped about the fate or whereabouts of jailed Russian opposition leader and Putin critic Alexei Navalny after his apparent disappearance six days ago.

The Kremlin said Tuesday that it does not track Navalny's location, with Putin's press secretary telling reporters: "We have neither the intention nor the ability to track the fate of prisoners and the process of their stay in the relevant institutions."

Navalny's allies said Monday that Navalny has been removed from the IK-6 penal colony in the Vladimir region, east of Moscow, where he has been imprisoned since last year, and that his whereabouts were unknown.

On Tuesday, Navalny's spokesperson said his location in the prison system remains unknown and he again did not show up at a court hearing by video link, Reuters reported. It's unclear whether Navalny was in transit to a new prison. Navalny was sentenced in August to an additional 19 years in prison on top of 11-1/2 years he was already serving.

The White House said it was "deeply concerned" by the reports of Navalny's disappearance. The Kremlin responded by saying that it considers "any intervention by anyone, including the United States of America, unacceptable and impossible."

— Holly Ellyatt

U.S. funding will not help Ukraine in its war efforts, Kremlin says

The upcoming meeting between U.S. President Joe Biden and his Ukrainian counterpart Volodymyr Zelenskyy will not impact circumstances on the battlefield or Russia's progress with its so-called "special operation," according to Kremlin spokesperson Dmitry Peskov.

"The tens of billions of dollars pumped into Ukraine did not help it; the new tens of billions are doomed to the same fiasco," he said in Google-translated comments carried by Russian state news agency Tass on Telegram.

Biden and Zelenskyy are set to meet at the White House later on Tuesday amid growing concerns over the U.S.' willingness to extend further funding to Kyiv. Ukraine has depended on Western allies for support and weaponry throughout its defensive campaign to fend off an ongoing Russian invasion into its territory.

The U.S. president wants Congress to approve $106 billion in supplemental spending, of which more than $61 billion would be earmarked for Ukraine, with the remaining financing split between close Washington ally Israel, border enforcement and humanitarian aid.

— Ruxandra Iordache

Russia says it discussed interstate agreement with Iran

Russia and Iran have agreed to speed up work on a large interstate agreement, the Russian foreign ministry said in a Google-translated press release, without disclosing further details of the deal.

The decision followed a Dec. 11 telephone exchange between Russian Foreign Minister Sergey Lavrov and his Iranian counterpart Hossein Amirabdollahian. A meeting readout from the Iranian foreign ministry published on social media did not directly reference the agreement.

The two foreign ministers also discussed the conflict between Israel and Hamas. Iran has historically sponsored the Palestinian militant group, with Moscow echoing current calls to implement a cease-fire and minimize civilian casualties in the Gaza Strip.

Russia and Iran enjoy a close relationship and anti-U.S. political stance, with Moscow frequently deploying Iranian-made Shahed drones in its war with Ukraine. Tehran denies having provided Russia weaponry for such a purpose.

Stripped of Western support and sanctioned, Moscow has increasingly been tightening relations with fellow oil-producing countries in the Middle East and with the world's second-largest economy, China. Russian President Vladimir Putin carried out two rare impromptu trips to Saudi Arabia and the United Arab Emirates on Wednesday, before receiving Tehran leader Ebrahim Raisi in Moscow on Thursday.

— Ruxandra Iordache

Zelenskyy makes 11th hour plea for Ukraine war funds in Washington

Ukrainian President Volodymyr Zelenskyy on Tuesday plans a last-ditch plea to U.S. lawmakers to keep military support flowing as he battles Russia, in visits to the White House and Capitol Hill.

Heading into winter, with tens of thousands of Ukrainians dead, a yawning budget deficit and Russian advances in the east, Zelenskyy is scheduled to press U.S. lawmakers to replenish nearly depleted funding, before meeting with President Joe Biden.

"If there's anyone inspired by unresolved issues on Capitol Hill, it's just (Russian President Vladimir) Putin and his sick clique," Zelenskyy said at a speech in Washington on Monday to a U.S. military audience.

Newly declassified U.S. intelligence shows that "Russia seems to believe that a military deadlock through the winter will drain Western support for Ukraine" and ultimately give Russia the advantage despite Russian losses, said Adrienne Watson, spokesperson for the White House National Security Council.

Ukraine is having success stopping Russian forces but Putin is continuing to order his troops forward despite heavy losses of troops and equipment since October, she added.

There are just three days before Congress recesses for the year on Friday, and Republicans in the House of Representatives have until now refused to pass a $106 billion supplemental bill that contains Ukraine aid without unrelated, fiercely disputed changes to U.S. immigration.

Putin, who said last week he would run for president again in 2024, is betting he can outlast Western aid and attention to score a major strategic victory against the West, Zelenskiy and Biden aides believe. The view is shared by European lawmakers who will send their own last-minute plea to Congress Tuesday.

Biden has cast the situation in stark terms, saying "history is going to judge harshly those who turn their back on freedom's cause."

Ultimately, U.S. troops could be forced to fight Russia, Biden and others warn, if an unchecked Putin invades a European ally covered by NATO's mutual defense commitments.

— Reuters

Russians could be slowly advancing around war hot spot Avdiivka

Russian forces could be slowly advancing in the area around the war hot spot of Avdiivka in the eastern Donetsk region, with Ukraine's military saying its forces had defended the area from the highest number of Russian attacks in one day on Monday.

Russian forces have been pressing to encircle the strategically important town, which is home to the largest coke producer in Ukraine, and nearby towns and villages, including Marinka.

Analysts at the Institute for the Study of War said Russian forces "continued offensive operations near Avdiivka on December 11 and recently marginally advanced" there and east of Stepove (1.8 miles northwest of Avdiivka).

Russian war bloggers, or "milbloggers," claimed on Dec. 11 that Russian forces made tactical advances in the railway area near Stepove and in northern Stepove, while one milblogger claimed that Russian forces entered the administrative borders of Avdiivka itself, but the ISW said it had observed no visual confirmation of any of these Russian claims.

Ukraine's General Staff reported Monday that "Ukrainian defenders continue to restrain the enemy who does not abandon attempts to surround Avdiivka."

"Our warriors are steadfastly holding the defense, causing the enemy significant losses," the General Staff said on Facebook, saying Ukrainian forces had repelled 42 attacks in the area to the east of Avdiivka on Monday, up from 36 Russian attacks the previous day. It recorded 14 attacks in the area around nearby Marinka.

Despite the significant increase in attacks compared with the past few weeks, analysts at the ISW said they have not observed significant Russian gains near Avdiivka.

— Holly Ellyatt

Ukraine counteroffensive hopes 'did not come true,' official says

Ukraine's counteroffensive hopes did not come true and the front-line situation remains "very difficult," according to a top Ukrainian security official.

A month before Ukraine launched its much-hyped counteroffensive in June, Oleksiy Danilov, secretary of the National Security and Defense Council of Ukraine, said it provided an "historic opportunity." Six months on, Ukraine has little to show for its mammoth efforts to attempt to retake Russian-occupied (and heavily fortified) land in the south and east of of the country.

Danilov told the BBC that expectations for the counteroffensive had not been met.

"There were hopes, but they did not come true. The fact that we have been defending our country for two years is already a big victory," he told the broadcaster.

Danilov acknowledged Kyiv had been overly optimistic about the counteroffensive, saying "people sometimes make mistakes. You cannot be an A-grader all your life."

It's widely accepted that the counteroffensive has failed in its objectives and few breakthroughs are expected as winter sets in, although it has showed few signs of constraining military activity so far with fighting as intense as ever in war hot spots in eastern Ukraine.

Russian forces are not only defending their entrenched positions — in Donetsk in eastern Ukraine, they've also been launching what even Ukraine describes as "significant offensive operations" around Avdiivka and Marinka in a bid to seize more of the region.

He described the current situation along an expansive front line as "very difficult" and said that the old "textbooks" for war, including NATO ones, "should be sent back to the archives."

"There hasn't been a war like the one we have in our country - not in the 20th nor the 21st Century," he said.

Amid concerns over future funding for Ukraine, Danilov said the armed forces would continue to fight come what may. "I can say for sure that we won't stop," he said. "We will continue fighting for our freedom, for our independence."

— Holly Ellyatt

U.S. expects more security assistance to Ukraine to be announced this month

U.S. National Security Spokesman John Kirby said Monday he expects the White House to announce additional security assistance for Ukraine, ahead of what it has described as a critical year-end deadline.

"We don't have too many more weeks left in this year to be able to provide security assistance, so I would fully expect that you're going to see us anounce additional security assistance before the end of the month," Kirby said.

His comments come ahead of talks between U.S. President Joe Biden and his Ukrainian counterpart Volodymyr Zelenskyy in Washington on Tuesday.

Intense negotiations are ongoing on Capitol Hill as the White House pushes to pass Biden's $110 billion package of wartime funding for Ukraine, Israel, and domestic border security.

Biden "will make it clear to President Zelenskyy that we're standing firm on this supplemental request, we absolutely need to get additional funding to support Ukraine going forward," and provide him with an update on the situation, Kirby said.

"He'll keep urging the negotiations forward, urging compromise, with the goal of getting all these national security issues fully funded as we need. They're all urgent, they're all important," Kirby told reporters on board Air Force One.

Kirby added that the talks come at a crucial time due to the situation in Ukraine.

"As winter approaches, we're seeing increased missile and drone attacks by the Russian armed forces against civilian infrastructure. We expect that that will continue, particularly against energy infrastructure, and as the Russian forces continue to try to take offensive action against hte Ukrainians all along that front, but particularly in the east," he said.

— Jenni Reid

Zelenskyy to meet IMF managing director while in Washington

Ukrainian President Volodymyr Zelenskyy is due to meet with International Monetary Fund chief Kristalina Georgieva in Washington on Monday, an IMF spokesperson told CNBC.

They said no further details could be provided at this point.

The IMF in March approved a four-year $15.6 billion loan program for Ukraine. Following the immediate release of $2.7 billion, the Extended Fund Facility (EFF) stipulated requirements for the country to enact reforms including raising tax revenues and strengthening anti-corruption measures.

The EFF includes a second phase requiring "more ambitious structural reforms to entrench macroeconomic stability, support the recovery and early post-war reconstruction, and enhance resilience and higher long-term growth, including in the context of Ukraine's EU accession goals," according to the IMF.

Zelenskyy is in Washington to hold talks with U.S. President Joe Biden and other top officials as he seeks to avoid a cessation or dramatic reduction in aid from the superpower before the end of the year.

— Jenni Reid

Russia's opposition leader Navalny reportedly removed from prison, whereabouts unclear

Russian opposition politician Alexei Navalny has been removed from the IK-6 penal colony in the Vladimir region, east of Moscow, according to posts from allies shared on his social media account.

The posts said his current whereabouts were unknown.

CNBC was unable to independently verify the reports.

Navalny's allies have been readying for his possible transfer to a tougher colony after he received a sentence to serve an additional 19 years in prison in August.

— Karen Gilchrist

Ukraine may need to cede some land to Russia, senator Vance says

Ukraine may need to cede some land to Russia in order to end the war taking place in its territory, Republican U.S. Senator J.D. Vance said Sunday, as backlash against the ongoing conflict rises among some Republican factions.

"What's in America's best interest is to accept Ukraine is going to have to cede some territory to the Russians, and we need to bring this war to a close," Vance, of Ohio, said on CNN's State of the Union.

The comments come as support for Ukraine wanes among some Republican lawmakers, who argue that the government's attention would be better directed toward its own national security issues.

— Karen Gilchrist

No green light for Ukraine's EU membership talks would be 'devastating,' Kuleba says

Ukraine's Foreign Minister Dmytro Kuleba said Monday that it would be "devastating" for both Ukraine and the European Union if EU leaders do not give his country the green light for membership talks at a summit later this week.

"I cannot imagine, I don't even want to talk about the devastating consequences that will occur shall the (European) Council fail to make this decision," Kuleba told reporters as he arrived for a meeting with EU foreign ministers in Brussels, according to Reuters.

— Karen Gilchrist

Putin unveils two new nuclear-powered submarines

Russian President Vladimir Putin on Monday unveiled two new nuclear-powered submarines that he said would soon start patrolling the Pacific, according to a Google-translated report from Russian state-owned TV network Zvezda.

In a televised event in the northern city of Severodvinsk, Putin inaugurated the vessels, which are named the Krasnoyarsk and Emperor Alexander the Third.

— Karen Gilchrist

Read CNBC's previous live post here:

Biden to host Zelenskyy at the White House; Ukraine may need to 'cede' territory, U.S. senator says