The U.S. Congress has called on President Putin to fully co-operate with Britain's investigation into the murder of former Russian security service officer Aleksandr Litvinenko. Britain wants main suspect Andrey Lugovoy extradited to face trial even thoug

The case has cooled relations between Russia and the U.K.

The move by U.S. politicians could put further strain on already-tense relations between Moscow and Washington. The U.S. administration believes the Russian government could have been involved in the poisoning of Litvinenko in 2006.

The former Russian security agent died after ingesting a rare isotope of polonium in London in November 2006.

London claims another former Russian agent, Andrey Lugovoy, committed the murder and is demanding his extradition from Russia. Moscow has refused the request, saying the Russian constitution bars extradition. Moreover, it says, Britain has not produced sufficient evidence to prosecute Lugovoy – now a Duma deputy.
 
Republican congresswoman Ileana Ros Lehtinen, who proposed the resolution which has been supported by Litvinenko's relatives, claims it is not just about the murder.

“Polonium 210 would prove to be a dangerous weapon that Islamic radicals could use seeking to inflict large numbers of civilian casualties and not just to murder an individual,” she explained.

The vote comes days before a scheduled meeting between George Bush and President Putin in Russia's southern resort of Sochi. Experts say this may not be the best time to pass such a resolution.

Andrew Kuchins of the Centre for Strategic and International Studies says Moscow should “collectively ignore the vote”.

“It is not clear whether President Bush and Condoleezza Rice will act at the behest of this recent resolution and urge Moscow to co-operate in the investigation,” he said.