A Russian court on Monday sentenced a 72-year-old American in a closed trial to nearly seven years in prison for allegedly fighting as a mercenary in Ukraine.

Prosecutors said Stephen Hubbard signed a contract with the Ukrainian military after Russia sent troops into Ukraine in February 2022 and he fought alongside them until being captured two months later.

He was sentenced to six years and 10 months in a general-security prison. Prosecutors had called for a sentence of seven years in a maximum-security prison.

Hubbard, from the state of Michigan, is the first American known to have been convicted on charges of fighting as a mercenary in the Ukrainian conflict.

The charges carried a potential sentence of 15 years, but prosecutors asked that his age be taken into account along with his admission of guilt, Russian news reports said.

Arrests of Americans have become increasingly common in Russia in recent years. Concern has risen that Russia could be targeting U.S. nationals for arrest to use later as bargaining chips in talks to bring back Russians convicted of crimes in the U.S. and Europe.

Also on Monday, a court in the city of Voronezh sentenced American Robert Gilman to seven years and 1 month for allegedly assaulting law enforcement officers while serving a sentence for another assault.

According to Russian news reports, Gilman was arrested in 2022 for causing a disturbance while intoxicated on a passenger train and then assaulted a police officer while in custody. He is serving a 3 1/2-year sentence on that charge.

Last year, he assaulted a prison inspector during a cell check, then hit an official of the Investigative Committee, resulting in the new sentence, state news agency RIA-Novosti said.

The U.S. and Russia in August completed their largest prisoner swap in post-Soviet history, a deal involving 24 people, many months of negotiations and concessions from other European countries, which released Russians in their custody as part of the exchange. Several U.S. citizens remain behind bars in Russia following the swap.