Alexander Mikhailov, a spokesman for the counterintelligence service, said that the man had been given special spy equipment and had been supplying secret military and economic information to Britain in exchange for money for more than a year.
The news came amid a cooling of relations between Russia and the United States over the arrest of a CIA official and his wife who are accused of spying for the Soviet Union and Russia.
Mikhailov said the man confessed on Jan. 25 that he spied for Britain, 10 days after he was arrested and charged with high treason, an offense which can carry the death penalty in Russia.
The information he provided contained details of Russian research into creating new weapons systems, their parameters and the amount of money being spent on such projects, Mikhailov said. The man's name was not released.
"On assignment for British intelligence for monetary reward, this Russian citizen collected and handed over information of a secret military and economic nature," Itar-Tass reported.
In London, the British Foreign Office said it had no comment on the arrest. The news came as CIA officer Aldrich Ames and his wife were to appear in a U.S. court Tuesday for a hearing on whether they should remain in jail until their trial. They were arrested on Feb. 21 and charged with selling secrets to the Soviet Union and Russia.
Responding to the expulsion of a U.S. diplomat from Moscow on Monday, the United States said it regretted the move, but had no plans to throw out another. "We regret the move because we are the aggrieved party," said Dee Dee Myers, spokeswoman for President Bill Clinton.
A U.S. Embassy counselor, named by Russian media as James L. Morris, was declared persona non grata following the expulsion from Washington of Alexander Lysenko, the chief of Russia's intelligence station in Washington.
Russian newspapers, commenting on the chilling of relations between the former Cold War foes, said that such a development was "inevitable."
"Five years of permanent talks about 'strategic partnership' have not brought partnership itself," the daily Segodnya said. "(The idea) did not work.
"The reason is plain: Both countries lack real 'partnership' interests. The last superpower, after being left alone, did not see reasons for equal cooperation with a fragment of its former great foe."(AP, Reuters, Itar-Tass)
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