"A team of investigators from the Prosecutor General's Office is currently questioning [Andrei] Lugovoi in the presence of Scotland Yard experts," the source told RIA Novosti, without specifying where the questioning would take place.
Litvinenko, an outspoken critic of President Vladimir Putin's administration and a close associate of fugitive oligarch Boris Berezovsky, died in a London hospital November 23. His body was found to contain a lethal dose of polonium-210, a radioactive isotope.
Dmitry Kovtun, a business partner of Lugovoi, was diagnosed with an illness also caused by radiation after meeting with Litvinenko in London in October.
Some media outlets have been circulating reports since Thursday that Kovtun's health has drastically deteriorated.
However, the Russian Prosecutor General's Office, which launched a criminal investigation Thursday into Litvinenko's death, and into a related murder attempt on Kovtun, said it had no information confirming such reports.
Experts from Scotland Yard arrived in Moscow Monday to interview people who met with Litvinenko around the time of his poisoning at the beginning of November.
