The latest claims emerged in a BBC program aired on Monday in the U,K. which quoted a senior British security official as saying there were "very strong indications" the London killing of Russian security service defector Alexander Litvinenko was a "state action" by Russia.
The comments were made on the same day that Russian President Dmitry Medvedev held his first meeting with British Prime Minister Gordon Brown, at the Group of Eight summit in Japan.
Yury Fedotov told RIA Novosti: "They should either dismiss these claims or confirm them. If they confirm these claims, we will have to review our priorities in bilateral relations with the U.K."
Alexander Litvinenko died of radioactive poisoning in London on November 23, 2006, three weeks after suddenly falling ill. British investigators accused Russian agent-turned-businessman Andrei Lugovoi over the murder, and demanded his extradition, sparking a major diplomatic row with Moscow.
Russian presidential aide Sergei Prikhodko said on Tuesday the timing of the British report was no coincidence, and was aimed at scuppering efforts to mend ties between the countries, the main theme of the leaders' discussions on Monday.
"We are trying to work to bring Russian-British relations out of this dead end. These various leaks and rumors show that unfortunately in Britain not everyone shares the constructive frame of mind that we have sensed from the prime minister," he said.
Meanwhile, Russia's top investigators said on Tuesday they had made significant progress in investigating the Litvinenko murder, and rejected new claims of the Kremlin's role in his death.