Staff Sergeant Gordon Black, 34, was arrested earlier this year in Russia’s Vladivostok after his girlfriend accused him of theft.
On Wednesday, a court in Russia’s far eastern city sentenced him to three years and nine months in prison on charges of stealing and making threats of murder, according to Russian news reports.
US officials and Russian authorities stated that Black flew to Vladivostok to visit his girlfriend and was subsequently arrested following her accusations.
Reports from Russian state news agencies Tass and RIA Novosti indicated that the Pervomaisky District Court judge also imposed a fine of 10,000 rubles (€112) on Black.
Prosecutors had initially sought a sentence of four years and eight months.
Black’s imprisonment adds strain to the already tense US-Russia relations, exacerbated by the ongoing conflict in Ukraine.
Moscow currently holds several Americans, including corporate security executive Paul Whelan and Wall Street Journal reporter Evan Gershkovich, both of whom the US government considers wrongfully detained.
Other detained Americans include musician Travis Leake and teacher Marc Fogel, both facing drug-related charges, as well as dual nationals Alsu Kurmasheva and Ksenia Khavana.
The US State Department has strongly advised American citizens against traveling to Russia.
Under Pentagon policy, service members require clearance for international travel, which Black did not obtain.
The US Army revealed that Black was on leave and returning to Fort Cavazos, Texas, from his station at Camp Humphreys in South Korea. He had not sought or received authorization for his trip to Russia.