Russian prosecutors have formally opened a criminal investigation into the poisoning death of former spy Alexander Litvinenko, and a related murder attempt on a Russian businessman, the Prosecutor General's office said on Thursday in a statement.

The statement said that the criminal investigation had been launched as a result of inspections, which revealed that Litvinenko died after being poisoned with a radioactive nuclide.

"The examination revealed that Litvinenko died after being poisoned with a radioactive nuclide, and (Dmitry) Kovtun, who met with Litvinenko in London in October 2006, was diagnosed with a disease also connected with a radioactive nuclide," the statement said.

Kovtun is the business partner of Andrei Lugovoi, whom Britain views as a key suspect in Litvinenko's death probe.

Traces of radiation have been detected in the hotel rooms in London where Lugovoi stayed in October and November, and on the airliners in which he flew to Britain, Russian daily Kommersant said on Wednesday.

The Russian chief prosecutor said on Tuesday that Russia would not extradite to Britain possible suspects in the poisoning death of Litvinenko but would help British police investigate the case.

British detectives went to Moscow this week as the investigation widened.

The Russian Prosecutor General's Office said that a team of its investigators may fly to London for investigations.

"We do not exclude that in case there is a need for a more detailed investigation of the circumstances of the case, a team from the Prosecutor General's Office may fly to Britain to work locally," Marina Gridneva, a Prosecutor General's Office official, was quoted by the Interfax news agency.

Also on Thursday, Russian Foreign Minister Sergei Lavrov said "The inquiry by Scotland Yard is not affecting our political relations."

However, he declined to comment on London's position on the issue and asked people not to politicize the case. "I cannot speak for Britain," he said.

"Attempts to spark a publicity campaign around this case and to turn it into a political sensation have been bogged down, including attempts by serious British media outlets," the minister added.

Lavrov said Russia had "expressed its readiness to help the investigators and was still committed to contributing to the investigation."

Litvinenko died of radioactive poisoning in London on Nov. 23. Experts investigating his death have found radiation traces at a dozen locations and on two British Airways planes that flew the Moscow-London route.

(Xinhua News Agency December 8, 2006)