Ryan Fogle, officially listed as a third secretary in the U.S. Embassy's political section, allegedly tried to recruit a Russian security official as a spy to get information on Tamerlan and Dzhokhar Tsarnaev, alleged to have carried out the April 15 bombings, Russian newspaper Kommersant said.
Tamerlan, 26, was killed in a police shootout three days after the bombing. Dzhokhar, 19, was wounded and later captured. He has been charged in the bombings and is being held in Devens, Mass., about 40 miles from Boston, at a federal prison medical facility at a former Army base.
The charges against him carry potential sentences of life imprisonment or the death penalty.
Both brothers lived in the Boston area but were born in Russia and had moved to the United States with their parents.
The marathon bombings killed three people and injured more than 260.
Kommersant linked Fogle's capture Monday night to a trip U.S. diplomats and FBI agents from Moscow took shortly after the bombings in coordination with Russian authorities to the capital of the Russian republic of Dagestan, in the North Caucasus region, to interview Anzor and Zubeidat Tsarnaev, the suspects' parents.
Kommersant did not indicate if Fogle was one of the diplomats.
Tamerlan Tsarnaev traveled to Dagestan last year and U.S. authorities are trying to find out if he built contacts in the area with local Islamist insurgents.
The CIA had no comment on the Kommersant report.
Fogle was declared persona non grata by the Russian Foreign Ministry Wednesday and ordered him to leave the country immediately.
He was arrested Monday night by Russia's Federal Security Service, known as the FSB, the main successor agency of the Soviet-era KGB.
The agents said he had made plans to recruit a Russian security officer as a spy, arriving at a residential area next to a park with a blond wig on his head, held in place by a baseball cap, and a brown wig in his knapsack.
The knapsack also held a compass, a Moscow street atlas, two pairs of sunglasses, a pocketknife and $130,000 in cash, and he was carrying a letter offering "up to $1 million a year for long-term cooperation," the FSB said.
Russia's Channel One broadcast a recorded phone call Wednesday in which a man identified as Fogle pushes for a face-to-face meeting with the security officer, saying it must take place immediately.
"I think it's worth meeting today," he says in the call, which the channel said was intercepted by the FSB. "It's impossible tomorrow, it's just only today. Well, it's worth, as I said, you can earn $1 million a year, and I have $100,000 with me, but it should be now."
A second call, minutes before Fogle and the officer met, has the man identified as Fogle saying: "Opposite you is the stairway to the park. I see you. I'll be there."
The channel, with close ties to the Russian government, said officers hung back until Fogle made contact with the recruit before seizing him.
Fogle was wrestled to the ground by the man he was trying to recruit. An FSB officer told the channel the targeted recruit was a combat officer "who had taken part in counter-terrorist operations many times himself in the North Caucasus, and himself had very serious military training."
U.S. Ambassador Michael McFaul was summoned to the Foreign Ministry Wednesday, where he was told once again about Moscow's outrage over what Russian officials called the failed CIA recruiting effort.
Moscow released a video showing a detained Fogle wearing the blond wig. It also showed photographs of the supplies Fogle allegedly carried to meet his recruit.
U.S. Secretary of State John Kerry declined to comment on the matter Wednesday after meeting with Russian Foreign Minister Sergei Lavrov Tuesday night on the sidelines of an Arctic Council meeting in Sweden.
"I have nothing to add with respect to the situation regarding an embassy official in Moscow," Kerry said. "And I am grateful to my friend Sergei Lavrov ... for a very productive meeting yesterday in which we did the large business of our countries, which was, first of all, the challenge of Syria."
Kerry and Lavrov did not discuss the spy case "since it is already public knowledge," the Russian Foreign Ministry quoted Lavrov as saying Wednesday.