The widow of the poisoned Russian dissident Alexander Litvinenko said yesterday that she had filed a lawsuit in the European Court of Human Rights to try to force Russia to find out who was behind his death.

On the first anniversary of her husband’s death, Marina Litvinenko vowed to intensify her campaign to bring Mr Litvinenko’s killers to justice. Lawyers for the family said that a scientific expert had established that the polonium210 used to poison Mr Litvinenko was likely to have originated in a Russian factory and could not have been purchased without the approval of the Russian State.

Speaking at a press conference, Mrs Litvinenko said that papers were filed on Thursday at the European Court of Human Rights, alleging that Russia was complicit in the murder and had a duty to investigate.

She said: “I want to know who was behind the killing of my husband. We need more official support. But I promise that one day we will know who’s responsible for this because without this knowledge we will never be safe.”

She said that she had gone to court because “diplomatic efforts to bring the murderers to stand trial in England are not likely to succeed”. British detectives have identified Andrei Lugovoi, a former KGB agent who met Mr Litvinenko on the day he was poisoned, as the main suspect, but he has protested his innocence and Russia has refused requests to extradite him to London.

Mrs Litvinenko said that she had one message for Mr Lugovoi: “[All] he has to do is go to London and represent himself in court. I am waiting for him in London.”

She claimed that Vladimir Putin, the Russian President, was giving protection “and in effect endorsement” to Mr Lugovoi. She said: “By doing so, Mr Putin has tainted his office, his Government and himself with this horrendous crime. He turned a murderer into a national symbol. At the very least, this makes him an accessory.”

Louise Christian, the Litvinenko family solicitor, said that an American nuclear expert working at a British university had testified in the court papers that the polonium used to poison Mr Litvinenko was “highly likely” to have come from the Avan-gard plant in Russia.

She said that the expert, whom she refused to name, had said: “If this is so, it is almost certain that the Russian State or its agents were responsible for the poisoning.”

Earlier in the morning, to commemorate Mr Litvinenko’s death, Alex Goldfarb, a friend of the family, read out his deathbed statement, in which he blamed Mr Putin for poisoning him and said that a “howl of protest” would forever echo in the Russian leader’s ears.

Standing outside University College Hospital in Central London, where Mr Litvinenko died, his father, Walter, also paid tribute to his son.

Straining to be heard over ambulance sirens, Mr Litvinenko said: “The gangsters who poisoned my son in the Millennium restaurant here are even today trying to show the whole world that they can get away with anything.

“As a reward, the chief executioner of my son, Mr Lugovoi, has now been given a seat in the Duma. Western leaders and European leaders must take these things seriously, because the gas and oil they buy from Russia may turn into something more sinister. I trust my son did not die in vain, and the truth and justice for which he was fighting will prevail in the whole of the world, including Russia.”

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