Russia has detained a U.S. citizen on spying charges that could land him in prison for as long as 20 years, the TASS news agency reported Monday.

TASS said Paul Whelan was taken into custody Friday "during a spy rally in Moscow," CBS News wrote.

The report said officers of Russia's domestic security service, the Federal Security Service (FSB), detained Whelan and opened a criminal case against him.

No details were offered about Whelan or the crimes he allegedly committed.

There was no immediate comment from the White House or U.S. State Department.

As UNIAN reported earlier, Maria Butina, an accused Russian spy who nuzzled up to the National Rifle Association before the 2016 U.S. election, has begun cooperating with federal prosecutors after agreeing to a plea deal in December.