Litvinenko Case 'Harming' U.K.-Russian Relations

Lavrov, speaking during a visit to Brussels, said it was "unacceptable" that a "campaign should be whipped up involving officials." He said both sides should avoid "politicizing" Litvinenko's death.

Shortly afterward, British Home Secretary John Reid said a team of British investigators had left for Moscow as part of a widening probe into Litvinenko's death.

"The police will, of course, as they do in all these cases, go where the evidence leads," Reid said. "And the [British] foreign secretary has already got assurances from her Russian colleagues and her opposite number that the Russian government will give us all the assistance that is necessary, and the police are already on their way to Russia and will go anywhere else that is necessary in order to investigate the circumstances of a suspicious death."

Litvinenko died last month after ingesting a quantity of the rare radioactive isotope polonium-210. In a deathbed letter, he blamed President Vladimir Putin for his death, but the Kremlin has denied any involvement.

(compiled from agency reports)