The FSB, the successor agency to the Soviet-era KGB, said Fogle was trying to recruit a Russian counterterrorism officer who specializes in the Caucasus, the volatile region in southern Russia where the two Boston Marathon bombing suspects have their ethnic roots.
Fogle, who was handed over to U.S. Embassy officials, was declared persona non grata and ordered to leave Russia immediately, the Foreign Ministry said. He has diplomatic immunity, which protects him from arrest.
It was the first case of an American diplomat publicly accused of spying in about a decade and seemed certain to aggravate already strained relations between Russia and the United States.
The Foreign Ministry summoned U.S. Ambassador Michael McFaul to appear Wednesday in connection with the case. McFaul, who was doing a question-and-answer session on Twitter when the detention was announced, said he would not comment on the spying allegation.
Russia's Caucasus region includes the provinces of Chechnya and Dagestan. The suspects in the Boston Marathon bombings are ethnic Chechen brothers and the elder brother spent six months last year in Dagestan, now the center of an Islamic insurgency.
U.S. investigators have been working with the Russians to try to determine whether suspected Boston bomber Tamerlan Tsarnaev had established any contacts with the militants operating in Dagestan.
Russian officials expressed indignation Tuesday that a U.S. diplomat would carry out such an espionage operation at a time when the presidents of the two countries have pledged to improve counterterrorism cooperation.
"Such provocative actions in the spirit of the Cold War do nothing to strengthen mutual trust," the Foreign Ministry said.
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 U.S. and sentenced to lengthy prison sentences.
On Tuesday, Russian state television showed pictures of a man said to be Fogle, wearing a baseball cap and a blond wig, lying face down on the ground. The man, without the wig, was also shown sitting at a desk in the offices of the FSB. Two wigs, a compass, a map of Moscow, a pocket knife, three pairs of sunglasses and packages of 500 euro notes ($649 each) were among the items the FSB displayed on a table.
The FSB also produced a typewritten letter that it described as instructions to the Russian agent who was the target of Fogle's alleged recruitment effort. The letter, written in Russian and addressed "Dear friend," offers $100,000 (â¬77,059.41) to "discuss your experience, expertise and cooperation" and up to $1 million (â¬0.77 million) a year for long-term cooperation. The letter also includes instructions for opening a Gmail account to be used for communication and an address to write. It is signed "Your friends."
Samuel Greene, director of the Russia Institute at King's College London, called the evidence bizarre.
"I wouldn't have thought that spies gave each other written instructions," he said in a telephone interview. Greene also noted that the FSB had displayed Fogle's official diplomatic ID, suggesting he was carrying it along with the spy paraphernalia when he was detained.
"Maybe this is what the CIA has come to, maybe the propaganda folks in the Kremlin think we are this stupid, or maybe both," he said.
A five-minute video produced by the FSB and aired on state television showed a Russian official speaking to what appear to be three American diplomats who had come to pick up Fogle in the FSB office. The official, whose face is blurred, alleged that Fogle called an unnamed FSB counterintelligence officer who specializes in the Caucasus at 11:30 p.m. on Monday. He then said that after the officer refused to meet, Fogle called him a second time and offered him 100,000 euros ($129,770) if he would provide information to the U.S.
The Russian official said the FSB was flabbergasted. He pointed to high-level efforts to improve counterterrorism cooperation, specifically FBI director Robert Mueller's visit to Moscow last week and phone calls between President Barack Obama and Russian President Vladimir Putin.
"At a time when the presidents of the two countries are striving to improve the climate of relations between the two countries, this citizen, in the name of the U.S. government, commits a most serious crime here in Moscow," the official said.
State Department spokeswoman Jen Psaki confirmed that an officer at the U.S. Embassy in Moscow was briefly detained and released.
"We have seen the Russian Foreign Ministry announcement and have no further comment at this time," said Psaki, who was in Sweden with Secretary of State John Kerry. The CIA declined to comment on the case.
Little was immediately known about Fogle. A third secretary is an entry level position at the State Department, the lowest diplomatic rank in the foreign service.
Putin has stoked anti-American sentiments among Russians in recent years in what is seen as an effort to bolster his support at home. He also appears to have a genuine distrust of Russian nongovernmental organizations that receive American funding, which he has accused of being fronts that allow the U.S. government to meddle in Russia's political affairs. Hundreds of NGOs have been searched this year as part of an ongoing crackdown by the Russian government.
Mark Galeotti, a professor at New York University who studies the Russian security services, said the public exposure of Fogle and the pictures splashed across Russian television suggest a political purpose behind the detention. He said these kinds of spying incidents happen with some frequency, but making such a big deal of them is rare.
"More often, the etiquette is that these things get dealt with quite quietly -- unless they want to get a message out," Galeotti said. "If you identify an embassy staffer who is a spy for the other side, your natural impulse is to leave them be, because once you identify, you can keep tabs on them, see who they talk to and everything else."
"There's no reason to make a song and dance, detain them, eject them," he said.
Greene said the American diplomat's detention should be seen as part of Putin's confrontation with the opposition and not as something likely to have a major impact on U.S.-Russia relations.
"I think this is mostly for domestic consumption in Russia so that people say, 'look at these naughty Americans trying to meddle in our internal affairs and spy on us,'" Greene said. "But everybody's got spies everywhere so I don't see this as a major issue."
In Washington, State Department spokesman Patrick Ventrell also said the incident was unlikely to hamper U.S.-Russia relations.
"I'm not sure I'd read too much into one incident one way or another," he told reporters, and pointed to Kerry's meeting with Russian Foreign Minister Sergey Lavrov in Sweden on Tuesday evening. "We have a very broad and deep relationship with the Russians across a whole host of issues, and we'll continue to work on our diplomacy with them directly."
Alexei Pushkov, who heads the international affairs committee in Russia's parliament, wrote in a Twitter post that the spy scandal would be short-lived and would not interfere in Kerry and Lavrov's discussions aimed at bridging deep differences over the civil war in Syria.
"But the atmosphere is not improving," Pushkov commented.
Associated Press writers Max Seddon in Moscow, Bradley Klapper in Washington and Lara Jakes in Kiruna, Sweden, contributed to this report.
Copyright 2013 The Associated Press.