The Litvinenko inquiry will "seriously complicate Russian-British ties", Russian Foreign Minister Sergei Lavrov said.
British government leaders could be sued for slander for their comments over the Litvinenko inquiry, Lavrov told a news conference.
The judge-led inquiry found President Vladimir Putin "probably" approved the assassination of former Russian spy Alexander Litvinenko in London.
Sir Robert Owen's report said Andrei Lugovoi and Dmitri Kovtun were probably acting under the direction of Moscow's FSB intelligence service when they poisoned him with radioactive polonium 210 at the Millennium Hotel in Mayfair in 2006.
He added he inquiry contained groundless accusations and left many questions unanswered.
The last day of the inquiry into Alexander Litvinenko's murder has heard that Vladimir Putin should be held responsible for his death.Read the full story ›
A suspect in the killing of Alexander Litvinenko,has been given until 9am today to give evidence to the inquiry into the Russian spy's death.
Dmitri Kovtun, has been accused of "manipulating" the probe after he was due to start giving testimony from Moscow by video link on Monday but has failed to do so as yet.
Mr Litvinenko, 43, died nearly three weeks after consuming tea laced with polonium-210 in London in November 2006.
Police concluded that the fatal dose was probably consumed during a meeting with Kovtun and Andrei Lugovoi at a hotel in central London.
Mr Kovtun had asked to give evidence but gave the inquiry a string of reasons why he was unable to in the days before he was due to appear again earlier this week.
A suspect in the killing of Alexander Litvinenko must confirm whether or not he will give evidence at the inquiry into the spy's death.Read the full story ›
One of the prime suspects in the killing of former Russian spy Alexander Litvinenko will give evidence at the inquiry into his death.Read the full story ›
One of the men accused of killing Alexander Litvinenko said he might have killed himself accidentally after handling radioactive material.Read the full story ›
A police officer investigating the death of ex-KGB agent Alexander Litvinenko has said the highest levels of radioactive contamination were recorded at the hotel where one of the prime suspects was staying.
Andrei Lugovoi, who, along with Dmitri Kovtun, are suspected of poisoning Mr Litvinenko with polonium-210 in 2006, was staying alone at the Sheraton Park Lane hotel between October 25 and October 28 that year.
Detective Inspector Craig Mascall has told the public inquiry into Mr Litvinenko's death that traces of radioactivity were found throughout the hotel and in Lugovoi's room.
The highest levels of radioactivity were discovered on towels, he said.
The inquiry also heard that a chaffuer-driven car used by Lugovoi to get out of London was found to have traces of radioactive contamination.
Lugovoi and Kovtun deny any involvement and remain in Russia.
Dmitri Kovtun's former wife appeared to contradict his own claim that he was a director of an oil company in 2006.
Mr Kovtun, who is accused of Alexander Litvinenko's murder, had fled to Hamburg in Germany and sought political asylum, the inquiry was told.
During an interview with British police in December 2006, Mr Kovtun listed his jobs as director general of gas and oil provider Global Project and an employee of Continental Petroleum Limited.
But in an extract of a police interview given by his ex-wife Inne Hohne, which was read to the court, she said he "wanted to be a porno star" and that he had "absolutely nothing to do with" the oil trade.
The inquiry into Alexander Litvinenko's death has heard how suspect Andrei Lugovoi was in hospital for exposure to radioactive material when Scotland Yard officers questioned him in Moscow.
Detective Inspector Craig Mascall from the Metropolitan Police's counter-terrorism unit told the inquiry that British officers travelled to Moscow to interview Mr Lugovoi and fellow suspect Dmitri Kovtun in December 2006.
Mr Mascall confirmed that both men are accused of murder and would be arrested if they ever entered the UK.
One of the men suspecting of murdering poisoned spy Alexander Litvinenko told police that anyone who caused damage to Russia should be "exterminated", the inquiry into his death has heard.
Former KGB officer Andrei Lugovoi is one of two men charged with Mr Litvinenko's murder.
In an extract of the newspaper interview shown to the inquiry, he said he believed Litvinenko was a "traitor".
He allegedly added: "If someone has caused the Russian state serious damage, they should be exterminated. This is my firm belief and the belief of any normal Russian".