Russia and the United States on Wednesday sought to limit the damage to already troubled ties from a new spy scandal that erupted when Moscow caught a blonde-wigged alleged CIA agent who was reportedly seeking information on the Boston bombings.
The suspected agent, who Moscow says was caught with a "typical espionage arsenal" of money and disguises, is said to have been working undercover as a low-ranking third secretary at the US embassy.
The man, named as Ryan C. Fogle, was caught red-handed in a blonde wig as he tried to recruit a Russian security agent with an advance of $100,000 for intelligence on the Northern Caucasus, according to the Russian FSB security service.
After being interrogated, he was handed back to the US embassy and ordered to leave the country after being declared persona non grata.
The Kommersant daily said that Fogle was likely to have been seeking intelligence about the Boston marathon bombers whose origins were in the Russian Northern Caucasus, despite pledges by security services to cooperate in the investigation.
US ambassador to Moscow Michael McFaul met officials at the Russian foreign ministry on Wednesday morning after being summoned to explain the presence of the alleged CIA agent.
The foreign ministry said that Deputy Foreign Minister Sergei Ryabkov had issued a protest to McFaul, confirming that Fogle had to leave in the "shortest possible time".
Nevertheless, both sides appeared keen to avoid inflammatory rhetoric at a time when they are engaged in sensitive diplomacy aimed at ending the conflict in Syria.
Russian Foreign Minister Sergei Lavrov steered clear of the topic, saying that he had opted not to bring up the case at talks in Sweden with US Secretary of State John Kerry.
"I decided that talking about it would be superfluous, since it is already made public and everyone already understands everything," he said in comments published on the ministry's website on Wednesday.
Former head of the FSB Nikolai Kovalyov described the alleged agent's interception as a great success for Russian intelligence as it was rare for spies to be caught red-handed, "all the more with such attributes as a wig".
Kovalyov, now a ruling party lawmaker, however predicted the episode would have no effect on bilateral relations.
"The Americans do nothing other secret services -- including ours -- would not do," he told the Interfax news agency.
Footage published by state English language television RT showed Fogle being pinned face down to the ground and having his hands put behind his back for the arrest, while apparently wearing a blonde wig under his baseball cap.
The FSB footage also displayed supposed espionage equipment including two wigs as well as a compass, a street atlas of Moscow and a somewhat old-fashioned mobile phone.
For all the comedy of the spy novel-style trappings of his kit, Kommersant daily said it was probable that Fogle was looking for information on the Tsarnaev brothers who are alleged to have carried out the marathon bombings.
It linked the agent's capture to a trip a US delegation made to Dagestan last month in coordination with the Russian authorities to investigate the April 15 blasts at the Boston marathon that killed three people and injured more than 260.
Suspected bomber Tamerlan Tsarnaev travelled to Dagestan in 2012 and US authorities are eager to see if he built up contacts with the local Islamist underground there.
"It is likely that during the trip in April the US side obtained the phone numbers of (Russian) Federal Security Service (FSB) agents," said Kommersant.
"Clearly, they then decided to use it to have personal contacts with anti-terror agents, given that the exchange of information in the form of questions and answers between special services is not always quick and smooth," it said.
US State Department spokesman Patrick Ventrell confirmed that an American staffer at the embassy had been briefly detained, but refused to respond to allegations that the man was an undercover CIA agent.