LONDON, November 23 (RIA Novosti) - Relatives and friends have paid tribute to Alexander Litvinenko, a former FSB officer and Kremlin critic who died in London exactly a year ago.

Litvinenko died after being poisoned with the radioactive element polonium-210. In a letter reportedly penned by Litvinenko on his deathbed, the dying man accused President Vladimir Putin of orchestrating his murder. The Kremlin strongly denied the accusation.

Vladimir Bukovsky, a one-time Soviet dissident and former friend of the murdered "Russian spy," said no public events had been planned for the anniversary.

"His relatives and friends will gather at the cemetery; we will stand at his grave and remember Alexander," Bukovsky said in London at a presentation of a collection of Litvinenko's articles and interviews.

A year after the event, a host of questions concerning the events of November 23, 2006 remain unanswered, with Russia continuing to deny any involvement in Livtinenko's death and disputing the so-called "polonium version".

Indeed, Moscow has launched its own inquiry into Litvinenko's murder, dismissing British investigators' evidence against their chief suspect, Russian national Andrei Lugovoi, as ungrounded and refusing to extradite him to the U.K.

Scotland Yard said Litvinenko received a fatal dose of polonium on November 1 while meeting with Lugovoi, a former Kremlin bodyguard-turned businessman, and his business partner Dmitry Kovtun at a luxury hotel in London. Kovtun was subsequently also hospitalized with polonium poisoning, although he later recovered.

Russia justified its refusal to extradite Lugovoi by saying that its Constitution did not permit the extradition of its nationals, offering instead to try the businessman within the country if sufficient evidence was provided.

The extradition dispute has strained relations between Russia and Britain, sparking a tit-for-tat row involving expulsions of diplomats and visa restrictions in July.

Andrei Lugovoi mocked British special services on Thursday at a press conference in the southwestern Russian city of Kursk, calling the Litvinenko case "a dismal failure of the British special services," adding that Britain had yet to present any evidence against him.

He also said Britain was telling 'barefaced lies' when it accused Russia of hindering the investigation into Litvinenko's death.

In further criticism, Lugovoi said Russian law enforcement agencies were investigating espionage activities by U.K. intelligence services in Russia, while the British Crown Prosecution Service was "hampering an objective investigation into these criminal cases."

Litvinenko's widow said earlier this week that she would sue the Russian government at the European Court of Human Rights in a bid to force Moscow to accept responsibility for her husband's death, as well as pay compensation.

Lugovoi said that by taking action against Russia, Marina Litvinenko was not seeking to establish the truth, but to cash in on a tragedy.

Marina Litvinenko's lawyers are likely to argue that the lethal polonium 210 used to poison her husband could have only been obtained by a state-sponsored group. They are expected to try and prove that that state was Russia.

In September, Lugovoi confirmed that he would run for parliament as a candidate for the Liberal Democratic Party, led by outspoken pro-Kremlin ultranationalist Vladimir Zhirinovsky. Under Russian law, a seat in the State Duma would give Lugovoi immunity from prosecution.