In a statement on Friday, FSB accused Eugene Spector, who was born in Russia and then moved to the US, of acting on behalf of the Pentagon.

“The American, acting in the interests of the Pentagon and a commercial organisation affiliated with it, collected and transferred to a foreign party various information on biotechnological and biomedical topics, including those constituting state secrets, for the subsequent creation by the US of a system of high-speed genetic screening of the Russian population,” the FSB said.

The details of the espionage case against Spector — who was already serving a three-and-a-half-year sentence in Russia for bribery — had been sparse.

Russian state news agencies reported on Tuesday that Spector had been handed a 13-year jail sentence for spying.

This was added to the existing bribery sentence and converted into a new 15-year jail term in a maximum security penal colony.

The FSB, which usually says if a defendant has confessed, did not say how Spector had pleaded in the closed-door proceedings.

The US Department of State said this week that it was aware of reports of the sentencing of a US citizen in Russia and was monitoring the situation.

The jailing of US citizens in Russia has been a major point of contention between Washington and Moscow as relations between the two countries have soured over the Russian invasion of Ukraine.

In August, more than two dozen people were freed in a prisoner exchange deal that involved nationals from several countries.

Wall Street Journal reporter Evan Gershkovich and former US Marine Paul Whelan — two American citizens jailed in Russia — were among those released.