Russian security services have held a US diplomat they claim is a CIA agent after catching him red-handed trying to recruit a Russian agent.
The FSB agency said that Ryan Fogle, a third secretary at the US Embassy in Moscow, was carrying special technical equipment, disguises, written instructions and a large sum of money when he was detained overnight.
State television showed pictures of a man said to be Fogle sitting at a desk in FSB offices.
The FSB said Fogle was handed over to US officials.
US ambassador Michael McFaul refused to comment.
Despite the end of the Cold War, Russia and the United States still maintain active espionage operations against each other.
Last year, several Russians were convicted in separate cases of spying for the US and sentenced to lengthy prison sentences.
The detention of Fogle, however, appeared to be the first American diplomat accused of spying in about a decade and seemed certain to aggravate already strained relations between the two countries.