The Russian government has warned that it would make an adequate response to Britain following the decision to expel four Russian diplomats from the UK.
In a televised statement, Russian deputy foreign minister Alexander Grushko said the British authorities would be informed of Moscow's response, but he did not disclose what that would be.
The decision to expel the Russian diplomats was announced yesterday by UK Foreign Secretary David Miliband after Moscow refused to extradite a former agent accused of murdering the dissident Alexander Litvinenko in London.
Mr Grushko bitterly criticised the decision to expel the diplomats over the incident.
He said that Mr Miliband had acknowledged in his Commons statement that the extradition of a Russian citizen to stand trial abroad would require a change to the constitution.
'We are being punished for observing our own constitution which is not just unfair and unacceptable but even contradicts common sense,' he said.
He pointed out that if Russia had responded in the same way each time an extradition request from Moscow was turned down by the UK, the British embassy in Moscow would be short of about 80 diplomats now.
