Andrei Lugovoi is wanted in the killing of Alexander Litvinenko, a former KGB agent poisoned last year with the radioactive substance polonium-210 after meeting Lugovoi and two other Russian men at a London hotel.

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

On his deathbed, the 43-year-old Litvinenko said Russian President Vladimir Putin was behind his killing, an allegation the Russian government rejected. Litvinenko had also said Russian authorities were behind a deadly 1999 apartment blast and the murder of investigative journalist Anna Politkovskaya.

Russia has said its constitution bars the extradition of nationals. But Britain is putting pressure on Moscow: the Foreign Office summoned the Russian ambassador Tuesday to urge cooperation.

Russia's First Deputy Prime Minister Sergei Ivanov suggested Wednesday that the Kremlin may not get involved in the case.

"We have a court, we have a prosecutor's office independent of the executive power that I hope will receive official materials" from Britain, Ivanov told a news conference.

He played down the potential for diplomatic repercussions in the standoff between Britain and Europe's leading energy supplier.

"I don't see a big connection between the Litvinenko case and the development of Russian-British relations on the whole," Ivanov said.

But a Blair spokesman warned that failure to produce Lugovoi risked worsening relations. He said Britain has received no formal response from Moscow, but declined to say whether Blair or Foreign Secretary Margaret Beckett planned to speak directly to their Russian counterparts about the case.