A Russian court has sentenced an American citizen to five years in prison on charges of illegally transporting a firearm, court officials said on Monday.

Charles Zimmerman, 58, was convicted by a court in the Black Sea resort city of Sochi after a gun was found on his yacht in June, according to the press service of the Krasnodar regional courts. The weapon was discovered during an inspection when the vessel arrived in Sochi.

Court records reviewed by The Associated Press showed that Zimmerman was convicted in October, and the verdict was upheld two months later by the Krasnodar regional court.

Zimmerman told the court that he had travelled to Russia to meet a woman he had contacted online and said he carried the gun for self-defence, unaware of Russian laws. The court said he fully admitted guilt.

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A website supporting Zimmerman describes him as a US Navy veteran, an electrician and a father of two. His family, however, has rejected the charges, calling them a “set-up” aimed at securing a future prisoner exchange.

His sister, Robin Stultz, said Zimmerman had been sailing from the United States to New Zealand and had no intention of entering Russia. She claimed he voluntarily declared the firearm and was then charged with arms smuggling.

There was no immediate comment from US officials.

Zimmerman is among several Americans still held in Russia following a series of high-profile prisoner swaps in recent years, as relations between Moscow and Washington remain at their lowest point since the Cold War.