Litvinenko friend seeks U.S. data on polonium

LONDON (Reuters) - A friend of poisoned Russian emigre Alexander Litvinenko has asked the U.S. Energy Department to reveal what he says it knows about the origin of the radioactive polonium that killed the former security officer.

Alex Goldfarb said he had filed the freedom of information request in a bid to prove the polonium was produced in Russia and support the allegation that Russian authorities were behind Litvinenko's death, something Moscow emphatically denies.

Litvinenko, an outspoken Kremlin critic, died in London in November 2006 after being poisoned with polonium that was slipped to him in a cup of tea.

The case has deeply damaged relations between Britain and Russia, which refused requests to extradite the chief suspect.

Goldfarb said the Department of Energy's Lawrence Livermore National Laboratory was the world's top nuclear forensics institute, and he knew from sources that Britain had sought U.S. help to analyze a sample of the polonium that killed Litvinenko.

In any sample, he said, "you have contamination with different isotopes, which is a tell-tale sign of the reactor that produced it. ... We hope to show the polonium originated in Russia."

Litvinenko's widow and her supporters allege the polonium came from Russia's Avangard plant, a state facility surrounded by tight security, and his killer could only have obtained it with official help.

Goldfarb said he expected his request to be fast-tracked by the Energy Department, on public interest grounds, after the Foreign Affairs Committee of the U.S. House of Representatives endorsed a resolution on Wednesday suggesting possible Russian government involvement in Litvinenko's death.

Goldfarb, a close associate of emigre Russian tycoon and Kremlin opponent Boris Berezovsky, heads a foundation whose declared aim is to secure justice for Litvinenko's family.

(Reporting by Mark Trevelyan, editing by Mary Gabriel)