MOSCOW, Jan. 3 (Xinhua) -- Russia has provided consular access to U.S. citizen Paul Whelan who was detained over spying, the Russian Foreign Ministry said in a statement on Wednesday.

The Russian Federal Security Service (FSB) arrested Whelan during a "spy act in Moscow" on Dec. 28 and has opened a criminal investigation over possible espionage.

The U.S. State Department said later that it was notified of the detention of Whelan and requested consular access and expected "Russian authorities to provide it."

The detention came after Russian citizen Maria Butina pleaded guilty in a Washington court on Dec. 13 to one conspiracy charge, admitting that she acted as an unregistered foreign agent to advance Moscow's interests.

Russian President Vladimir Putin said that Butina has no ties to Russian intelligence services, and that the whole case against her was unfounded.