The widow of Russian dissident Alexander Litvinenko has launched an appeal for donations to help her expose her husband's murderers at the inquest into his death.
Marina Litvinenko said her legal costs for the inquest, which is set to consider claims that the Russian state was behind the former KGB spy's assassination, were likely to run into hundreds of thousands of pounds.
Mr Litvinenko, 43, fell ill shortly after drinking tea during a meeting at a West End hotel with former KGB contacts and died of radioactive polonium-210 poisoning in London's University College Hospital on November 23 2006.
St Pancras coroner Dr Andrew Reid indicated on Thursday that the dissident's inquest should be wide-ranging and announced he was asking the Metropolitan Police and intelligence agencies MI5 and MI6 to carry out further inquiries.
Mrs Litvinenko appealed to the public in Britain, Russia and around the world for assistance in funding her legal battle to discover what really happened to her husband.
She said in a statement: "I am prepared to do whatever it takes to find the truth about the unprecedented act of nuclear terrorism that killed Sasha (Alexander) Litvinenko and endangered the lives of thousands of my fellow Londoners.
"To judge from inquests of similar complexity, such as those into the deaths of Princess Diana and the victims of the 7/7 bombings, these hearings may last weeks, if not months.
"At the very least, my legal costs are likely to run into six figures.
"In these proceedings the evidence collected by the Metropolitan Police will be weighed against the story presented by Sasha's accused murderer and his sponsors, with the unlimited resources of the Russian state at their disposal.
"I am sure that my legal team is the best in the world, but the reality is that compared to my adversaries I am severely constrained. This I why I am appealing to the public for help."
The UK's relations with Russia soured after the murder of Mr Litvinenko, who had accused Russian security services of carrying out terror attacks to help bring Vladimir Putin to power.
British prosecutors have named fellow ex-KGB agent Andrei Lugovoy as the main suspect in the dissident's killing, but the Russian authorities have repeatedly refused to send him to face trial in the UK.
Russian president Dmitry Medvedev insisted during Prime Minister David Cameron's visit to Moscow last month that Mr Lugovoy - now a Russian MP - would never be extradited to Britain.
Former director of public prosecutions Lord Macdonald QC said earlier this month that he had the "gravest suspicion" that Moscow was involved in planning the murder.
:: Donations to Mrs Litvinenko's legal fund can be made through the Litvinenko Justice Foundation website, http://www.litvinenko.org.uk