The newly appointed head of Russia's National Investigation Committee, Alexander Bastrykin, criticized Britain's Scotland Yard for focusing on one suspect -- Russian businessman Andrei Lugovoi -- while ignoring other possible leads, Russian news agencies reported.
He said investigators had "other versions," and when asked if Berezovsky could have been involved, said, "We are not ruling out such a version."
Berezovsky, a Kremlin critic, lives in self-imposed exile in London.
Britain is seeking the extradition of Lugovoi to face trial for the murder of Litvinenko, who died of radiation poisoning in London in November.
Lugovoi has denied any involvement and last month accused Britain's foreign intelligence service, Berezovsky, or the Russian mafia of being behind the murder.