British officials seeking to prosecute a former KGB bodyguard for murder worked Wednesday on a formal extradition request which Russia has already said it will reject.

Andrei Lugovoi is accused of killing Alexander Litvinenko, a former KGB agent turned Kremlin critic who allegedly was poisoned with a radioactive substance during a meeting with Lugovoi in London.

Prime Minister Tony Blair's office urged international law to be respected. Russia, however, said its law prohibiting the extradition of its nationals trumped any international agreement.

"An extradition request will be drawn up and it will be forwarded to the Russian government by our embassy in Moscow," said a Foreign Office spokesman, speaking on condition of anonymity in line with government policy.

Russia's ambassador in London was summoned to the Foreign Office on Tuesday, but the spokesman refused to discuss any further contacts which may be under way. "Obviously, we have regular contact with the Russian Embassy in London anyway," he said.

Radioactive traces were found at a dozen sites across London after Litvinenko's death Nov. 23, including three hotels, a soccer stadium, two planes and a business block used by self-exiled Russian tycoon Boris Berezovsky. More than 1,000 people in Britain and abroad were tested for polonium-210 contamination.

On his deathbed, the 43-year-old Litvinenko accused President Vladimir Putin of being behind his killing. Litvinenko had also accused Russian authorities of being behind a deadly 1999 apartment blast and investigative journalist Anna Politkovskaya's murder.

The Russian government has denied all involvement in Litvinenko's death.

A senior U.S. intelligence official, speaking on condition of anonymity, said that the U.S. intelligence community is divided over who ordered Litvinenko's murder, and why.

Some analysts, the official said, think Litvinenko — as well as Politkovskaya who gunned down in Moscow in October — were killed because of their criticism of the war in Chechnya.

Others think Litvinenko's killing was part of a campaign against the Kremlin's opponents in the run-up to Russia's parliamentary elections in December and the presidential contest in March 2008. Another theory is Litvinenko was the victim of a personal feud.

Relations between Britain and Russia have long been sour.

Britain has refused to hand over Russian exiles, including Berezovsky — once an influential Kremlin insider who fell out with Putin and fled to Britain in 2000 to avoid a money-laundering investigation — and Chechen opposition leader Akhmed Zakayev.

It has also complained of growing numbers of Russian spies in Britain. Russia last year passed a law that allowed for security forces to use force abroad against people considered threats.

Britain's ambassador to Russia, Anthony Brenton, has complained of being stalked by a pro-Kremlin Russian youth group called Nashi which wanted him to apologize for participating in an opposition conference last year.

Russia's Federal Security Service accused four British diplomats of spying after a state-run television report said British diplomats had contacted Russian agents using communications equipment hidden in a fake rock in a Moscow park.

The most delicate issue, however, is energy.

Britain exports oil and gas but depleting supplies have raised concerns about future reliance on the Gulf states and Russia.

The EU gets a third of its oil and about 40 percent of its natural gas from Russia.

One fifth of the world's gas reserves are in Russia and are controlled by Gazprom, the giant Russian utility. Gazprom, which already has a minor presence in Britain, is targeting 20 percent of the domestic gas market by 2015.

Lugovoi joined the KGB in 1987 after serving in the Kremlin guard corps. During his time in the KGB he provided security for Prime Minister Yegor Gaidar and for Berezovsky.

He now has a security company and has interests in producing the Russian drink kvas.

"I consider this decision to be political, I did not kill Litvinenko," Lugovoi said.

Prosecutor said Lugovoi could be tried in Russia — a scenario dismissed by Litvinenko's widow, Marina.

"Everything that happened, happened here," she said.