His ministry later said that the alleged reports of Russian spies operating in the United States were groundless, and that "such actions are ungrounded and have unseemly goals."

"We do not understand the reasons why the U.S. Department of Justice has made a public statement in the spirit of the Cold War," said ministry spokesman Andrei Nesterenko.

Meanwhile, head of the Russian Foreign Intelligence Service, Sergei Ivanov, on Tuesday declined to comment on the incident.

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Russia and some Western powers have repeatedly traded accusations of running spying operations despite the end of the Cold War. Yet the latest one came at a sensitive timing.

The incident broke out on the heels of Russian President Dmitry Medvedev's visit to the United States last week, during which presidents of the two countries went out for cheeseburgers, walked side by side in a park and agreed to "reset" the relations between the two old rivals.

"In any case, it is regrettable that all these things are happening on the background of the 'reset' in Russian-U.S. relations announced by the U.S. administration," said Nesterenko.

U.S. authorities said that the bust of the alleged Russian spy group wrapped up a multi-year investigation, during which investigators intercepted a message from Russian intelligence services to two of the accused, ordering them to "search and develop ties in policymaking circles" in the United States.

In a report back to Moscow, one defendant allegedly reported the change of CIA director, information gained from a private conversation with a former legislative counsel for Congress.

Court documents also said one suspect was instructed to build relationship with a New York financier well-connected in the political circles.

In a related development, Britain and Ireland said on Tuesday they are probing reports that fraudulent British and Irish passports were used by the alleged Russian spies.