Four Russian diplomats expelled in the row over the extradition of Andrei Lugovoi to face murder charges have left the UK, the Russian embassy says.
Andrei Lugovoi has denied involvement in the murder
The UK announced the expulsion after Moscow refused to hand over Mr Lugovoi, who is suspected of poisoning ex-KGB agent Alexander Litvinenko in London.
Russia responded to the announcement by expelling four UK embassy staff.
These included the head of the British Embassy's economic section, Andrew Levi, media reports said on Thursday.
The British Embassy in Moscow has refused to confirm reports that Mr Levi is expected to leave the country on Sunday, saying it will not comment on the identities of those expelled.
A 10-day deadline set by Britain on 16 July for the Russian diplomats to leave the country has expired.
The Russian Embassy said the four had left the country but did not specify when this had happened. The names of the expelled Russian diplomats have not been made public
The British diplomats were also given 10 days to leave Russia. This deadline expires on 29 July.
The UK's director of public prosecutions has recommended Mr Lugovoi be tried for murder by "deliberate poisoning".
Mr Litvinenko, who had taken UK citizenship, died of exposure to radioactive polonium-210 in London in November 2006.
Traces of the radioactive isotope were found in several places visited by Mr Lugovoi, who denies any involvement in Mr Litvinenko's death.
Under the European Convention on Extradition 1957, Russia has the right to refuse the extradition of a citizen while its constitution expressly forbids extraditions.
The UK has the right to request Mr Lugovoi be tried in Russia, but the UK's director of public prosecutions, Sir Ken Macdonald, has already turned down the offer.