Nine British detectives are in Moscow investigating the radiation poisoning death in London of dissident former Russian spy Alexander Litvinenko.
Members of Russia's prosecutor general's office met Tuesday with the Scotland Yard investigators. A Russian statement said the sides established areas of cooperation.
Prosecutor General Yuri Chaika said the British team will not make any arrests on Russian soil, and said no Russian suspects will be extradited to Britain. He said the British detectives will not interview leaders of Russia's Federal Security Service, and said only Russian authorities will directly question figures in the case.
Separately, the Interfax news agency quoted Russian prison officials as saying they will not allow the Britons to interview an imprisoned Russian security operative who claims Russian agents plotted to kill Litvinenko and other Kremlin foes.
The agent, Mikhail Trepashkin, is serving a four-year term for divulging state secrets.
In a statement Litvinenko's colleagues say he wrote on his death bed, the dying agent accused President Vladimir Putin of ordering his assassination.
Mr. Putin dismissed the allegation, and Monday, Russian Foreign Minister Sergei Lavrov warned that continued speculation of Kremlin involvement in the death may damage relations with Britain.
Meanwhile, the Times of London newspaper quotes British intelligence sources as saying they are convinced that Russia's Federal Security Service orchestrated a "highly sophisticated plot" to kill Litvinenko.
An autopsy found the deadly isotope polonium 210 in Litvinenko's body.
Some information for this report was provided by AFP, AP and Reuters.