Russia has reacted angrily to US claims that it has broken up a Russian spy ring operating in the country, saying that American police were "out of control," and that the accusations were "baseless and improper".
Moscow has admitted that the suspects are Russian citizens, but Vladimir Putin, the Russian prime minister, was heavily critical of the arrests in comments directed at Bill Clinton, the former US president, who is on a visit to Russia.
"Back at your home, the police went out of control [and] are throwing people in jail," Putin said.
"We don't understand the reasons which prompted the US department of justice to make a public statement in the spirit of Cold War-era spy stories.
"I hope that all the positive gains that have been achieved in our relationship will not be damaged by the recent event."
'Baseless and unfounded'
Ten suspected spies were arrested in Boston, New York, New Jersey and Virginia on Sunday and accused of recruiting political sources and gathering information for the Russian government.
An 11th man was arrested in Cyprus on Tuesday, after immigration officers discovered his name on a stop list, police said.
Christopher Robert Metsos, who was bailed as he awaits an extradition hearing, was identified as a Canadian national but was holding a US passport, police said.
Russia's foreign ministry has described the allegations, which include charges of conspiracy to act as an agent for a foreign government and money laundering, as unfounded.
"Such actions are baseless and improper," a statement from the ministry said.
The US state department has tried to play down fears that the arrests could jeopardise relations with Moscow, which have improved in recent months.
"We're moving towards a more trusting relationship. We're beyond the Cold War," Philip Gordon, a state department official said.
"I think our relations absolutely demonstrate that. But as I say, I don't think anyone was hugely shocked to know that some vestiges of old attempts to use intelligence are still there.
"We have from the start focused on the reason for the reset in the relations and the common interest, and I think we will continue to do so."
'Signal to Moscow'
The timing of the operation has stunned observers, coming a week after a successful visit to the US by Dmitry Medvedev, the Russian president, during which he was described by President Obama as a "solid and reliable partner".
The two held talks at the White House after Medvedev had visited California's Silicon Valley, and both leaders attended the G8 and G20 meetings over the weekend in Canada.
|Obama, left, recently said US-Russia ties had been 'reset' after meeting Medvedev [AFP]
Alexander Nekrassov, a former Kremlin advisor, told Al Jazeera that the case would likely have shocked the Russian government.
"I think Moscow was stunned because after such a glorious visit, something like this comes. I suspect that some people couldn't believe what was happening," he said.
"We can assume that this is a signal to Moscow that the American government is not really happy with certain policies and certain issues that have been discussed."
According to court papers unsealed on Monday, the defendants had been operating in the US for years, with alleged activities ranging from as far back as 2000 to just Saturday, when undercover FBI agents met two of the accused individuals.
They were not assigned to collect classified, secret information, a justice department official said, but were allegedly tasked to learn about a broad swath of topics including nuclear weapons, US arms control positions, positions on Iran, White House rumours, CIA leadership turnover, the last presidential election, congress and political parties.
Intelligence on Obama's foreign policy positions, particularly as they related to Russia, appeared to have been one of the top priorities for the defendants, according to the court filings.
'Deep cover agents'
There was no clue in initial court papers about how successful the so-called agents had been, but they were alleged to have been long-term, deep cover spies, some living as couples.
Deep cover agents take civilian jobs with no visible connection to a foreign government, rather than operating from government jobs inside embassies and military missions.
Al Jazeera's Cath Turner travelled to the suburb of Yonkers, where two of the suspects were seized.
She said the area was what one would expect of a middle class American suburb - green and leafy, with nice houses and friendly neighbours.
"The general pattern that seems to be happening is that neighbours don't suspect a thing, and people are completely stunned that this could be happening in their neighbourhood," she said.
Vicky Pelaez, one of the alleged spies arrested in Yonkers, was a columnist with El Diario-La Prensa, a Spanish-language newspaper in New York, and had won acclaim as a television reporter in her native Peru.
She had written commentaries that were critical of American foreign policy.
Juan Lazaro, her husband and another arrestee, had been a professor who criticised US wars in Afghanistan and Iraq while supporting Hugo Chavez, the Venezuelan president and US foreign policy opponent.
FBI agents said in court papers that the defendants communicated with alleged Russian agents using mobile wireless transmissions between laptops computers while they were close to each other.