The Russian Foreign Ministry considers a U.S. report on the arrest of a group of suspected Russian spies controversial, a ministry spokesman said.
"We are looking into the reports; they are controversial and require further clarification," the spokesman said without providing any further details.
The U.S. Department of Justice said in a statement on Monday that 11 people had been charged as "unlawful agents of the Russian Federation within the United States."
Eight of the suspects were arrested on Sunday as allegedly being deep cover Russian agents in the United States. Two others were arrested for allegedly participating in the same Russian intelligence operation, while one suspect remains at large.
The U.S. announcement came only a few days after Russian President Dmitry Medvedev's visit to the United States and may cast a shadow on improved bilateral relations between the two countries.
U.S. media sources have said it is unclear from the report what information was transmitted by those charged and whether their activities jeopardized U.S. security.
The Justice Department said the defendants were also charged with "conspiracy to commit money laundering."
According to U.S. law, those found guilty of conspiracy to act as an agent of a foreign government without notifying the U.S. Attorney General face a maximum penalty of five years in prison. Those found guilty of conspiracy to commit money laundering face 20 years.
The U.S. authorities said the case was "the result of a multi-year investigation conducted by the FBI, the U.S. Attorney's Office for the Southern District of New York, and the Counterespionage Section and the Office of Intelligence within the Justice Department's National Security Division."
According to the complaint filed in the court by U.S. intelligence, some of the suspects had been under surveillance since January and part of their correspondence with the Center in Moscow had been intercepted and decoded.
"You were sent to USA for long-term service trip. Your education, bank accounts, car, house etc - all these serve one goal: fulfill your main mission - to search and develop ties in policymaking circles in the U.S. and send intels," one of the intercepted messages allegedly said.
The FBI also reported observing various espionage techniques used by the agents to communicate with their handlers, varying from old-fashioned "drops" in parks and faked identification papers to hi-tech electronic encoding.
The evidence submitted by the FBI to the court indicates that some of the suspects were in contact with Russian "state officials," including diplomats from Russia's Permanent Mission to the United Nations in New York from 2004 to the beginning of 2010.
MOSCOW, June 29 (RIA Novosti)