Both countries are conducting parallel investigations into the death of Litvinenko, who died of radioactive poisoning in London, on November 23, 2006.
In an interview published today by the Russian daily "Izvestia," Zvyagintsev said Britain has failed to give Russia the same level of cooperation as British detectives received when they traveled to Moscow in late 2006 to question witnesses.
Russia wants to interview more than one hundred people in Britain, including Russian emigres wanted for trial in Moscow.
Zvyagintsev, however, says Britain has given Russian investigators clearance to interview Boris Berezovsky, a Russian tycoon who is wanted in Russia on corruption charges and has been granted asylum in Britain.
Litvinenko was an associate of Berezovsky.