|The UK government says it found evidence of Russian intelligence service activities against British interests [EPA]
Russia has criticised Britain for expelling a diplomat from its London embassy for spying, calling the move groundless and saying Moscow had been forced to respond in kind.
The mutual diplomatic expulsions between Russia and Britain are the first since 2007, when relations fell to a low after Alexander Litvinenko, a Kremlin critic, was killed in London with a rare radioactive isotope.
"The British side took an unfriendly step the other day, having groundlessly declared one of our colleagues in our embassy in London persona non grata," Russia's foreign ministry said in a statement on Wednesday.
"We were forced to take an adequate corresponding measure."
It did not say what the measure was, but the UK has said Russia requested the removal of a British diplomat on December 16 and that both diplomats had now been withdrawn.
The latest spat undermines efforts by Britain's new coalition government to forge a better relationship with Russia.
|The death of Litvinenko in 2007 sparked a lingering diplomatic row between Russia and the UK [Reuters]
Britain has said it requested the expulsion of the diplomat on December 10 after evidence of Russian intelligence service activities against British interests.
"There is clear evidence of activities by Russian intelligence services against UK interests," a British foreign ministry spokesman said on Wednesday.
There had been recent signs of a thaw with the British government which took power in May.
David Cameron, the British prime minister, last month accepted an invitation to visit Russia next year and William Hague, his foreign minister, has already been to Moscow.
Relations have been further strained by a conflict between BP and its billionaire Russia-connected partners in the TNK-BP venture, whom the British oil company accused of using connections with Russian authorities to win a row over strategy and management control in 2008.
The dispute resulted in the departure of TNK-BP's then chief executive Robert Dudley from Russia in 2008 under what he described as unprecedented pressure from authorities.
In the same year, the Russian government forced the closure of some of the British Council's regional offices - the British government's cultural centres - saying they were not legal.