MOSCOW (AP) — Russian prosecutors asked for a seven-year sentence in the trial of a U.S. citizen accused of fighting as a mercenary in Ukraine against Russia, Russian news agencies reported Saturday.

Prosecutors asked the court to take into account 72-year-old Stephen Hubbard's age and said he has admitted guilt, according to Interfax. They asked that Hubbard serve the sentence in a maximum-security penal colony.

In Russia, participating in mercenary activities is a criminal offense punishable by imprisonment for a term of 7-15 years.

Prosecutors accuse Hubbard of signing a contract with the Ukrainian military after Russia sent troops into Ukraine in February 2022, for which he allegedly was to receive at least $1,000.

He reportedly underwent training, received a personal firearm and fought in the Ukrainian military as a mercenary until April 2022, when he was detained by the Russian military.

The U.S. Embassy in Moscow told The Associated Press it was "aware of the reports of the arrest of an American citizen," but said it could not comment any further "due to privacy restrictions".

Russian courts convict more than 99% of defendants, and prosecutors can appeal sentences that they regard as too lenient.

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 later use as bargaining chips in talks to bring back Russians convicted of crimes in the U.S. and Europe.

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 who released Russians in their custody as part of the exchange. Several U.S. citizens remain behind bars in Russia following the swap.