Litvinenko, 44, who defected in 2000, died in London November 23. Doctors said a lethal dose of radioactive polonium-210 was found in his body. Before his death, Litvinenko accused the Kremlin of orchestrating his poisoning in a deathbed note, a charge that President Vladimir Putin strongly denied.
Detectives from Scotland Yard and the Russian Prosecutor General's Office have been investigating the case in London and Moscow.
"We have made a list of over 100 people whom we want to interview in Britain, including Russians living there. Moreover, we are seeking permission to examine a number of facilities and conduct other investigative procedures," Alexander Zvyagintsev told Izvestia daily.
He said work had already begun, adding that the list included tycoon Boris Berezovsky, who lives in London as a political emigre.
Earlier, Berezovsky, who is wanted in Russia on charges of fraud and attempts to overthrow the Russian government, said he would meet with Russian investigators in London only if his security was guaranteed.
Zvyagintsev said British law enforcement agencies had given no official information on the involvement in the poisoning of agent-turned-businessman Andrei Lugovoi, a key witness in the Litvinenko case.
Lugovoi and another witness, former security service agent Dmitry Kovtun, met with Litvinenko in a London hotel shortly before he was hospitalized with symptoms of poisoning, and have themselves undergone radiation checks. Both have denied any involvement in Litvinenko's death.