WASHINGTON, April 2 (RIA Novosti) - The U.S. House of Representatives has unanimously endorsed a resolution that urges the Kremlin to aid Britain in the investigation into the death of Russian security service defector Alexander Litvinenko.

The resolution on Litvinenko, who died of radioactive polonium poisoning in London in November 2006, was proposed by Republican Congresswoman Ileana Ros Lehtinen and calls on President George W. Bush and Secretary of State Condoleezza Rice to urge Moscow to cooperate in the investigation into his death.

The resolution also notes that "97 percent of the world's legal production of polonium-210 occurs at the Avangard nuclear facility in Russia, and Russia is the world's leading exporter of polonium-210 for commercial purposes."

"The murder of Mr. Litvinenko, a political dissident who was forced into exile by the Russian Government, is cause for great alarm," Ros-Lehtinen said last week. "The Russian government should cooperate fully with British investigators and ensure the security of radioactive materials."

Bush may now raise the issue of Litvinenko's death during his meeting with Russian President Vladimir Putin in Russia's Black Sea resort city of Sochi on April 6.

The Litvinenko Justice Foundation said in a statement released in London on Monday that Marina and Walter Litvinenko, the widow and father of the former Russian security service member, had sent letters to the leaders of the U.S. House and Senate saying the resolution was important for promoting "justice and security."

When debating on the resolution, Howard Berman, the chairman of the House of Representatives Foreign Affairs Committee, said that Litvinenko's death raised "disturbing questions about how elements of the Russian government appear to deal with their enemies."

Litvinenko was fired from the FSB (formerly the KGB) following a 1998 press conference in which he and a number of other FSB men alleged that they had been ordered to murder and kidnap a number of high-profile figures.

London has requested the extradition of its chief suspect in the Litvinenko case, Russian businessman and MP Andrei Lugovoi. Moscow has refused to extradite the former Kremlin security guard, saying its Constitution does not permit this. Lugovoi, who met with Litvinenko in London before he fell ill, denies any involvement and says Litvinenko tried to recruit him for the British Secret Intelligence Service (MI6).

The dispute has led to a dramatic deterioration in relations between London and Moscow, including tit-for-tat expulsions of diplomats and the closure of two British Council offices in Russia.

Litvinenko received British citizenship in 2006 and published two books in Britain alleging the involvement of the Russian security services in a series of apartment bombings in Russia in 1999. He also wrote about this topic in Russia for Novaya Gazeta, the newspaper that Anna Politkovskaya was working for at the time of her murder in 2006.