A U.S. Army solider stationed in South Korea was accused of theft and arrested in Vladivostok, Russia, on May 2, according to the Army.

Why it matters: The U.S. and Russia are already negotiating over other arrested Americans who the U.S. has deemed wrongfully detained, and the arrest of Staff Sgt. Gordon Black could escalate tensions between the two countries further.

The latest: Black was assigned to Eighth Army at Camp Humphreys in northwest South Korea but in recent days was given leave to visit Fort Cavazos, Texas, Army spokesperson Cynthia Smith said in a statement Tuesday.

• Instead of returning to Texas, Black flew from Incheon, South Korea, to Vladivostok for personal reasons without requesting official clearance to do so, Smith said.
• Smith added that the Army notified Black's family after Russian authorities contacted the U.S. Embassy in Moscow about his arrested.

Zoom in: Black had a personal relationship with a Russian woman from Vladivostok, according to TikTok videos of the couple posted by the woman.

• In one, she referred to Black as her "husband," Radio Free Europe/Radio Liberty reported.

Zoom out: Black enlisted in the Army in 2008 and was deployed to Iraq from October 2009 through September 2010 and to Afghanistan from June 2013 until March 2014, according to Smith.

• His mother, Melody Jones, told "Good Morning America" in an interview that she did not feel comfortable about Black traveling to Russia to visit his girlfriend.
• Jones said she did not know if he had a visa to visit Russia and said he was questioned for nine hours after arriving.
• "I cry at night. I'm hoping he's not being tortured or hurt," she said, according to ABC News.

The big picture: Several Americans are currently being held in Russia, including Wall Street Journal reporter Evan Gershkovich, former Marine Paul Whelan and Radio Free Europe/Radio Liberty journalist Alsu Kurmasheva.

• The U.S. State Department has deemed Gershkovich and Whelan wrongfully detained.
• The department has repeatedly urged Americans to leave Russia and has warned that it appears the Russian government is targeting Americans for detention.

Go deeper: Russia announces tactical nuclear weapon drills as tensions with West spike

Editor's note: This story has been updated with additional details.