Staff Sergeant Gordon Black, 34, had been assigned to the Eighth Army, based at Camp Humphreys in South Korea, and was set to change duty stations to Fort Cavazos in Texas, Army spokeswoman Cynthia Smith said in a statement. He processed out of the Eighth Army on April 10, signing out on leave. But instead of returning to the US, he flew from South Korea’s Incheon Airport to Vladivostok, Russia, via China.

“Black did not request official clearance, and DoD did not authorize his travel to China and Russia,” Smith said, noting restrictions currently in place on both official and leave travel. “There is no evidence Black intended to remain in Russia” after his leave ended, she said.

A Russian interior ministry official informed the US embassy in Moscow on May 3 that Black had been arrested a day before for “theft of personal property,” Smith said, without providing further details. The sergeant is being held in pretrial detention, where he will remain until his next hearing.

An Army official, speaking on condition of anonymity to discuss a sensitive matter, confirmed an NBC report that Black had traveled to Russia to visit a girlfriend in the country.

Tass, the Russian state news agency, quoted regional police as saying a complaint was filed by a woman who had been “in a relationship with the foreign citizen who she met in South Korea, where she was working.” After the man came to visit her in Vladivostok, according to the Tass account, they had a conflict at her home and “after he left, the woman discovered that money was missing and went to the police.”

Among Americans held in Russia are businessman Paul Whelan and journalist Evan Gershkovich, both of whom the US classifies as wrongfully detained. Both have been charged with — and Whelan convicted of — espionage charges that they and the US government dismiss as false.