

An American citizen has been arrested in Moscow on suspicion of espionage, Russia's domestic security service, the FSB, said on Monday.

The agency identified the man as Paul Whelan. A criminal case has been opened against him.

"On December 28, staff members of the Russian Federal Security Service detained US citizen Paul Whelan in Moscow while on a spy mission," the FSB said in a statement on its website. No other details were given.

CHRISTOPHER FURLONG/GETTY IMAGES Russia's state security service, the FSB, says it has detained an American citizen suspected of spying in Moscow.

By Russian law, foreigners found guilty of spying on Russia face between 10 and 20 years in prison.

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The arrest of the US citizen comes as tensions between Washington and Moscow continue to escalate over a range of issues from election meddling to the crises in Syria and Ukraine.

Earlier this month, Russian gun rights activist Maria Butina pleaded guilty to conspiring with a senior Russian official to infiltrate US conservatives. Butina, 30, is the first Russian national to be convicted of seeking to influence U.S. policy in the run-up to the 2016 election by acting as a foreign agent.

Shortly before her guilty plea, Russian President Vladimir Putin said Butina was not known to any of his spy agencies. The country's Foreign Ministry has gone to great lengths to paint Butina as a political prisoner, notably by launching a wide-ranging social media campaign.

The State Department could not be immediately reached for comment.