LONDON - Britain expelled a Russian diplomat suspected of spying Tuesday, and Russia responded by expelling a Briton in the latest skirmish in a long-running spat over espionage.

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Foreign Secretary William Hague said Britain had asked the Russian Embassy in London to withdraw a staff member on Dec 10 "in response to clear evidence of activities by the Russian intelligence services against UK interests."

Russia, in return, expelled a diplomat from the British Embassy in Moscow.

"We reject any basis for this action," Hague said in a statement. The two staff left their posts in London and Moscow on Monday night, his office said.

A British government official, speaking on condition of anonymity, said Russian officers had "crossed the line" of what was deemed acceptable. The official declined to expand, but insisted that the British diplomat had no ties to Britain's intelligence community.

The Russian Foreign Ministry and the Kremlin refused to comment when contacted by the Associated Press.

UK-Russia relations soured after the 2006 poisoning death in London of former Russian agent Alexander Litvinenko. Russia has refused to extradite Britain's main suspect in the case, former KGB officer Andrei Lugovoi.