Russian Foreign Ministry Spokesman Mikhail Kamynin on Thursday said four British embassy staff in Moscow are now persona non grata and they should leave the territory of the Russian Federation within 10 days. He did not identify the diplomats.
British Ambassador to Russia Tony Brenton said he was summoned to the Russian Foreign Ministry and given "certain messages" to deliver to London.
"I met with Deputy Minister [Alexander] Grushko, and we of course discussed the Litvinenko case," the Interfax news agency reported Brenton as saying. "He gave me several notices for me to pass on to London."
Brenton would not comment on the messages' contents, the Russian agency reported.
Britain has been waiting for the "appropriate response" Russia promised to deliver after four Russian diplomats were expelled on Monday. The diplomatic clash began last week when Russia refused to extradite Andrei Lugovoi, a suspect in the murder of Kremlin critic and former KGB agent Alexander Litvinenko.
According to the British public prosecutor, ex-KGB officer Lugovoi is said to have killed Litvinenko by poisoning him with radioactive polonium-210 in November 2006. Lugovoi has denied involvement in the case.
Russia, however, rejected European Union assertions that Moscow had not cooperated with British authorities in the Litvinenko case.
Russia's EU envoy Vladimir Chizhov told Interfax that while British investigators were quickly given permission to travel to Russia as part of their probe, Russian authorities were prevented from entering Britain for some time.
Mikhail Kamynin said earlier that diplomatic sanctions announced by Britain earlier this week would have "the most serious consequences" for relations between Moscow and London.
"The position towards Russia taken by the new Labour government of Great Britain is based on anything but common
sense or pragmatism and respect of law, which is so typical of
real Britons," Kamynin added on Thursday.
Russia was also going to stop issuing visas to British officials, Kamynin said, adding that shared security and terrorism efforts would also be affected.
"To our regret, cooperation between Russia and Britain on issues of fighting terrorism becomes impossible," he said, describing Russia's response as "targeted, balanced and the minimum necessary."
The British Foreign Office had earlier said that no retaliation by Russia would be justified, and officials from both countries, however, said on Tuesday that the current row, which the Russian pressed has termed a "diplomatic war" would not affect economic ties.