Foreign Ministry spokesman Mikhail Kamynin said the British ambassador in Moscow had been given official notice that four British Embassy staff members are now considered persona non grata and should leave the territory of the Russian Federation "within 10 days."
Kamynin did not identify the four diplomats to be expelled.
The measures announced by Russia today mirror almost precisely those threatened by Britain in response to Moscow's refusal to extradite Andrei Lugovoi, a key suspect in the murder of former security service officer Aleksandr Litvinenko.
In addition to the diplomats' expulsion, Britain said it was taking steps to limit cooperation on visa and security issues.
Kamynin said today Russia, too, was ceasing cooperation on security issues and taking "reciprocal action" on visa issues.
Until Britain specifies what visa restrictions it will impose, he said, "Russian officials will not apply for British visas, nor shall we consider similar visa applications by British officials."
'Minimally Required Steps'
Kamynin said he believed "common sense would prevail" in the ongoing dispute between Britain and Russia. But he defended Moscow's decision as appropriate and necessary.
"As you see, Moscow is taking targeted, weighed, and minimally required steps," he said. "We were compelled to take such steps, considering the deliberate choice that London has made to worsen relations with our country."
British Foreign Secretary David Miliband said Britain was disappointed that Moscow has failed to cooperate on Lugovoi's extradition and criticized today's announcement as unfair.
"We obviously believe that the decision to expel four embassy staff is completely unjustified, and we will be doing everything to ensure that they and their families are properly looked after," he said.
Miliband added, however, that Britain was "heartened" by the support it had received from the international community.
Just minutes before Kamynin's announcement, U.S. Secretary of State Condoleezza Rice told Britain's Sky News that Russia should honor Britain's request for Lugovoi's extradition.
Russian Foreign Minister Sergei Lavrov tomorrow travels to Berlin for talks with his German counterpart, Frank-Walter Steinmeyer, on issues including the extradition dispute.
Relative Restraint?
Russia earlier this week threatened "serious consequences" to the British measures and said it was within its rights to expel as many as 80 diplomats from Moscow.