Britain is expelling four Russian diplomats and exploring other retaliatory measures after the refusal by Moscow to send former intelligence officer Andrei Lugovoi to London for trial in the murder of his former colleague, Alexander Litvinenko. Moscow says the British move will lead to serious consequences when Russia responds. For VOA, Tom Rivers reports from London.

British-Russian relations have taken a frosty turn with the decision by London to expel a number of Russian diplomats after Moscow's refusal to extradite the main suspect in the murder of Alexander Litvinenko.

Former Russian intelligence officer Litvinenko died last November after being poisoned with the radioactive substance, polonium-210 in the British capital.

Among the last people he met on the day he became ill was a former colleague of his, Andrei Lugovoi.

Lugovoi has repeatedly denied any involvement in Litvinenko's death, and Moscow has formally told London that a request for his extradition could not be fulfilled as it would be in breach of the Russian constitution.

In the House of Commons, Foreign Secretary David Miliband underlined that the British government continues to take matter very seriously.

"Our aims are clear," said Mr. Miliband. "First, to advance our judicial process, second, to bring home to the Russian government the consequences of their failure to cooperate and third, to emphasize our commitment to promoting the safety of British citizens and visitors."

Given the impasse, Mr. Miliband outlined a number of measures London will impose on Moscow.

"First, we will expel four diplomats from the Russian embassy in London," he said. "Second, we shall review the extent of our cooperation with Russia on a range of issues and as an initial step, we have visa facilitation negotiations with Russia and made other changes to visa practice."

"Third, international agreements mean Mr. Lugovoi could be extradited to the UK if he traveled abroad. Fourth, we are grateful for the strong support we have received from EU [European Union] partners and close allies, including through the EU presidency statement on the first of June. We will discuss with partners the need for future EU-Russian engagement to take up concerns on this case into account," he continued.

Russia promises to give what it calls an "adequate response" to the British expulsion order. Part of that response may come in the form of reprisal tit-for-tat expulsions and a return to cooler relations in general.