Russia on Monday again denied any involvement in the murder of Alexander Litvinenko and challenged Britain to present any evidence to the contrary.
The reaction came in response to an article, entitled "Russia murdered Litvinenko, says top prosecutor," published in The Sunday Times.
It said Lord Macdonald of River Glaven, the chief prosecutor who investigated the murder of Alexander Litvinenko by radioactive poisoning, has spoken publicly for the first time of his suspicion that the killing was a "state directed execution" orchestrated by Russia.
In a letter to the editor, Konstantin Shlykov, press secretary the Russian Embassy to London, dismissed the allegations as "not being supported by evidence."
"We are sure that such evidence has never existed. Otherwise, it would have been presented to us," he said.
"I am sure that the assertion that the murder of Mr Litvinenko was a 'state directed execution orchestrated by Russia' is another big lie, which someone wanted to disseminate in 2006," Shlykov said.
"Now we must try to find the truth together. Russia is no less interested in doing so than Great Britain."
Lord Macdonald unsuccessfully asked Russia to extradite Andrei Lugovoi, the prime suspect, to Britain.
"I had the gravest suspicion that Russian state actors were involved in the planning of this murder," he said, adding that "it had all the hallmarks of a state directed execution, committed on the streets of London by a foreign government, according to The Sunday Times.
Lord Macdonald charged Lugovoi, now an MP in his homeland, with Litvinenko's murder. His request to have Lugovoi extradited was refused by Russia, the paper said.
Litvinenko, a former KGB officer and outspoken critic of then-president Vladimir Putin, died in November 2006 in a London hospital after being poisoned with the radioactive substance polonium-210.
British police suspect ex-KGB bodyguard Andrei Lugovoi of the murder. Russia rejected British requests to extradite Lugovoi, citing its Constitution, which does not permit the extradition of Russian nationals. The row led to a drastic deterioration in bilateral relations.