Russian First Deputy Prime Minister Sergey Ivanov has said the dispute over Alexander Litvinenko's murder has not strained ties with the UK.

"There's no connection between the Litvinenko case and UK-Russia relations," Ivanov told a news conference.

Andrei Lugovoi, a former KGB officer, is accused of the murder of Litvinenko who died in London last year because of exposure to the radioactive isotope, polonium-210.

The UK has called on Russia to extradite Lugovoi to face trial. A formal request for the extradition will be presented to the Russian authorities before the end of the week.

Ivanov said Russia hopes to receive official documents on the case from the UK so that Russian prosecutors can make "an independent decision" about the extradition request "based on the constitution and Russian laws."

The Russian prosecutor-general's office says, according to the constitution, Russian citizens cannot be handed over to foreign countries for prosecution but can appear in a domestic court "backed by the evidence provided by the foreign state."

Lugovoi has strongly denied any involvement in the case and accuses the British media of demonising him, saying the UK's request is "politically motivated" describing the charges as "completely unfounded."