The European Union is urging Russia to cooperate with Britain in a diplomatic dispute over a probe into last year's murder of ex-Russian spy Alexander Litvinenko.

Portugal, which currently holds the EU presidency, issued a statement Wednesday expressing "disappointment" with what it says is Russia's failure to work with Britain.

Britain this week expelled four Russian diplomats because of the Kremlin's refusal to extradite former intelligence agent Alexander Lugovoi - the chief suspect in the Litvinenko murder. Russia says its constitution forbids extraditing citizens.

Moscow has promised to retaliate. Litvinenko died of radiation poisoning last year, weeks after meeting Lugovoi in a London hotel. Lugovoi denies involvement.

Also Wednesday, British police announced the arrest and deportation to Russia of a suspect in an alleged plot to murder exiled Russian billionaire Boris Berezovsky.

Police say they arrested the suspect last month and turned him over to immigration authorities. They did not identify him.

Berezovsky briefly fled Britain in June for his own safety.

The Russian tycoon has accused the Kremlin of ordering his and Litvinenko's death - charges the Kremlin denies. Russia is demanding Britain extradite Berezovsky for trial for alleged fraud. London granted him asylum in 2003.