Media reports said that person could be Italian academic Mario Scaramella, although they could not be independently confirmed.
Scaramella met with Litvinenko in a London restaurant just hours before Litvinenko fell ill on November 1.
Scaramella has previously denied that he had been poisoned and that he had anything to do with Litvinenko's death. He told a Rome press conference on November 22 that he had received e-mail threats days before Litvinenko's poisoning and met the former Russian intelligence officer to discuss the threatening email.
Investigators are hoping that an autopsy today of the body of Litvinenko could shed some light on the investigation -- in particular when and how he managed to ingest the radioactive substance.
Russia's nuclear energy chief, Sergei Kiriyenko, was quoted as saying today that polonium-210 cannot be obtained illegally in Russia.
Litvinenko, a British citizen who died on November 23, was a fierce critic of the Kremlin and Russian President Vladimir Putin. In a note made public after his death, Litvinenko accused Putin of killing him.
The Kremlin and the Russian secret services have denied any link with his death.
Weeks before his death Litvinenko was caught on camera at a London journalists' club accusing Putin of ordering the killing of journalist Anna Politkovskaya.
"I'm totally confident that only one person in Russia could kill someone like Anna Politkovskaya with her standing, with her fame, and that is Putin," Litvinenko said.
Another prominent Russian political figure has fallen ill with suspected poisoning.
Ireland's police force says it has opened an investigation into how former acting Russian Prime Minister Yegor Gaidar may have been stricken with illness during a visit to Ireland.
A police statement said detectives would seek to trace Gaidar's movements before he fell violently ill during a conference in Dublin on November 24.
Gaidar's spokesman, Valery Natarov, said his boss's life is not in danger and his condition is improving.
Doctors in Moscow, where Gaidar is now recovering, said on November 30 that they saw no natural cause for his ailment.
His daughter says that her father could be released from hospital as soon as next week.
Public Health Fears
Meanwhile, investigators continue to examine other locations where radiation has been found.
Addressing the U.K. parliament on November 30, Home Secretary John Reid said that 24 venues were being monitored, and experts had confirmed traces of contamination in around 12 of these venues.
Around 1,700 people have reportedly called a government-run hotline saying they were at locations Litvinenko supposedly visited the day he fell ill.
Traces of an undetermined radioactive substance have also been found in several passenger planes. Two British Airways planes under investigation had flown between London and Moscow. A third British Airways plane will fly back from Moscow today for radiation tests.
The U.K. airline has said that up to 33,000 people could have come in contact with a radioactive substance.
U.K. Foreign Secretary Margaret Beckett pressed her Russian counterpart Sergei Lavrov today over the need for Moscow to assist with the Litvinenko investigation.
However, Lavrov was quoted by Interfax as saying that Russia had not received any formal enquires from the United Kingdom.