A U.S. soldier was detained in Russia last week, a U.S. Army spokesperson said in a statement.
The soldier, Staff Sgt. Gordon Black, had been stationed in South Korea and traveled to Russia on his own and not on official business, according to four U.S. officials.
He had finished his deployment and was heading back to the U.S. when he made a side trip to Vladivostok, Russia, to visit a woman he was romantically involved with, officials said. They added that he had traveled there without permission from his superiors and is now being held in pre-trial confinement.
The soldier is accused of stealing from a woman, the officials said. It was not immediately clear if it was the same woman he was visiting.
Get top local stories in Philly delivered to you every morning. >Sign up for NBC Philadelphia's News Headlines newsletter.
The soldier was detained Thursday, U.S. Army spokesperson Cynthia O. Smith said in a statement.
Smith said the soldier was apprehended in Vladivostok "on charges of criminal misconduct."
U.S. & World
Stories that affect your life across the U.S. and around the world.
"The Russian Federation notified the U.S. Department of State of the criminal detention in accordance with the Vienna Convention on Consular Relations," Smith said. "The Army notified his family and the U.S. Department of State is providing appropriate consular support to the Soldier in Russia. Given the sensitivity of this matter, we are unable to provide additional details at this time."
Rep. Michael McCaul, R-Texas, chairman of the House Foreign Affairs Committee, said he is "deeply concerned" by reports that a soldier was detained in Russia.
"Putin has a long history of holding American citizens hostage," McCaul said in a post shared on X. "A warning to all Americans—as the State Department has said, it is not safe to travel to Russia."
Current travel guidance from the U.S. State Department restricts travel for citizens to Russia. "Exercise increased caution due to the risk of wrongful detentions," according to the State Department advisory. The Pentagon also restricts travel for Defense Department personnel.
Black is one of a number of Americans detained in Russia, including several civilians.
Arrests of Americans in Russia have increased as the relationship between the two countries has sunk to Cold War lows, The Associated Press reported. The U.S. has accused Russia of targeting Americans and using them as bargaining chips, according to the AP.
Among the most prominent U.S. citizens to be detained are Wall Street Journal reporter Evan Gershkovich, who was jailed last March, and former Marine Paul Whelan, who was arrested in 2018. The U.S. government has said that both Gershkovich and Whelan are wrongfully detained.
WNBA star Brittney Griner spent 10 months in Russian penal colonies for drug-related charges but was released in a rare prisoner exchange for Russian arms dealer Viktor Bout in 2022.
This is a developing story.
This story first appeared on NBCNews.com. More from NBC News: