Litvinenko, 44, an outspoken Kremlin critic with close ties to exiled oligarch Boris Berezovsky, defected in 2000 and received a British passport shortly before his death in London November 23. Doctors said a lethal dose of radioactive polonium-210 was found in his body.
The Russian embassy in the U.K. told RIA Novosti that a representative of the Russian Prosecutor General's Office will stay in the British capital until February 24.
"He will have meetings with colleagues from Scotland Yard in preparation for the arrival of the investigative group who will conduct further investigations," the embassy said Monday.
Before his death, Litvinenko accused the Kremlin in a deathbed note of orchestrating his poisoning, a charge that Putin strongly denied.
Detectives from Scotland Yard and the Russian Prosecutor General's Office have been investigating the case in London and Moscow, where key witnesses, Andrei Lugovoi and another former security service agent, Dmitry Kovtun, are based.
Russia's top prosecutors earlier ruled out that Lugovoi, whom British media have called the key suspect in the Litvinenko case, could be extradited to the U.K., saying he was a Russian citizen and could not be tried elsewhere.
Earlier, Berezovsky, wanted in Russia on charges of fraud and attempts to organize a coup, said he could meet with Russian investigators in London only if his security is ensured.
"First, it [the meeting] cannot be held in the Russian embassy, as I don't trust the Russian authorities, they are ready for any provocation," he said then. "And second: before the meeting, Prosecutor General's Office representatives must be searched for any poisonous substances or weapons."
