There have been reports in the Western media suggesting that Honor and Dignity, a foundation of veterans of Russia's intelligence and diplomatic services, might have been involved in Litvinenko's death.
The spokesman, who asked that his name not be used, dismissed assertions that foundation President Valentin Velichko, a former Federal Security Service (FSB) officer, might have had a part in the Litvinenko case.
"That is groundless, unsubstantiated information," he said, adding the group is pondering a lawsuit against the media outlets that made the allegations.
British investigators arrived in Moscow Monday to interview people who met with Litvinenko around the time of his reported poisoning by radiation in early November.
Dmitry Kovtun, a business partner of key witness Andrei Lugovoi, was questioned Tuesday, Lugovoi's lawyer, Andrei Romashov, said. Kovtun met with Litvinenko on the day he fell ill.
A source close to Lugovoi, a businessmen and former officer of the Federal Protection Service, said earlier that investigators might not be able to question the key witness, who is still undergoing medical checks.
U.S. TV channel ABC News said Wednesday, citing an unidentified British official, that investigators were treating Lugovoi as the main suspect in the November 23 death by radiation poisoning of Litvinenko, who defected from Russia in 2000 and was known as an outspoken Kremlin opponent.
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 the UK, the popular Russian daily Kommersant said Wednesday.
ABC also claimed Russian authorities have hindered British investigators' efforts in Moscow.