Russia on Tuesday said it had detained an alleged American CIA agent who was working undercover at the US embassy and was discovered with a large stash of money as he was trying to recruit a Russian intelligence officer.

Russia's Federal Security Service (FSB, ex-KGB) identified the man Ryan C. Fogle -- third secretary of the political section of Washington's embassy in Moscow -- and said he had been handed back to the embassy after his detention.

The FSB said it questioned Fogle before releasing him to the US embassy.

The FSB said in statement carried by Russian news agencies that Fogle was carrying "special technical equipment, written instructions for recruiting a Russian citizen, a large sum of money and means for changing a person's appearance."

The statement added that "recently, the US intelligence service has made repeated attempts to recruit the staff of Russian law enforcement agencies and special services, which were detected and carried out under control of the Russian FSB counterintelligence service."

The Russian news agency reports said the suspected agent had been caught red-handed trying to recruit an employee of one of the Russian security services.

The incident comes amid a new chill in Russian-US relations sparked by the Syria crisis and concern in Washington over what it sees as President Vladimir Putin's crackdown on human rights.

The last major spy row between the two former Cold War rivals involved the glamourous Anna Chapman and 10 other Russian spies in 2010.

All were arrested in the US and deported to their home countries.