London, England (CNN) -- The United Kingdom expelled a Russian diplomat on suspicion of spying, and Russia kicked out a British embassy staffer in Moscow in retaliation, the British Foreign Secretary William Hague said Tuesday.
Britain asked the Russian to leave on December 10 "in response to clear evidence of activities by the Russian intelligence services against UK interests," he said in a statement.
Russia told the British diplomat to leave Moscow on December 16, he said, but denied there was "any basis" for the expulsion.
Both embassy staffers have now been withdrawn, Hague said.
There has been no official Russian Foreign Ministry reaction, but a Russian source said the matter was "routine" and hoped London and Moscow would be "reasonable."
A Russian aide to a British lawmaker was arrested recently and faces deportation, but that case is not connected to the embassy expulsions, the Foreign Office said.
"The deportation case against Katia Zatuliveter is entirely unconnected to this issue," it said in a statement.
Zatuliveter, an aide to Liberal Democrat Member of Parliament Mike Hancock, was arrested December 2 and is facing expulsion from the UK, Hancock said.
"She is not a Russian spy," he said. "I know nothing about espionage, but she has been subjected to a deportation order. She is appealing it because she feels -- quite rightly -- that she has done nothing wrong."
London's Sunday Times newspaper said the British intelligence service MI5 determined that the 25-year-old is a Russian sleeper agent.
CNN's Matthew Chance and Richard Allen Greene contributed to this report.