Russian authorities are again accusing Britain of efforts to recruit a Russian citizen as a spy.
The director of Russia's Federal Security Service (FSB), Nikolai Patrushev, told reporters his agency is investigating the case, but did not identify who was involved.
Earlier this month, Russian officials said they are probing charges by former KGB agent Andrei Lugovoi that exiled Russian tycoon Boris Berezovsky and poisoned Russian intelligence agent Alexander Litvinenko were British spies.
Britain has accused Lugovoi of killing Litvinenko, but Russia refuses to extradite him.
Lugovoi, who met with Litvinenko in London last November, on the day the former spy fell ill, maintains his innocence in the death.
He also said the British spy agency may have played a role in Litvinenko's poisoning by radioactive polonium-210. In a deathbed statement, Litvinenko accused Mr. Putin of ordering his poisoning, a charge the Kremlin denies.
Lugovoi also suggested that Berezovsky might have been behind the killing. Many Russian officials have said Berezovsky, an exiled critic of Mr. Putin, masterminded the murder as a way to damage the Kremlin's reputation.
Some information for this report was provided by AFP, AP and Reuters.