Alexander Litvinenko's widow has spoken of her ongoing heartache as she marked five years without justice for the Russian dissident.
Marina Litvinenko said time had run out for his "killers" to reveal the truth and she spoke of her regrets over damaged relations between Russia and Britain.
The 49-year-old said she was confident an upcoming inquest would cement claims of Russian state involvement in the former KGB spy's death.
As she attended a private ceremony in his memory, she urged former KGB contacts Andrei Lugovoy and Dmitry Kovtun to "show some courage" by flying to the UK to face the coroner's questions.
"My patience has run out," she added. "But I believe this inquest will bring the truth."
Mrs Litvinenko was joined by her son, Anatoly, 16, and Boris Berezovsky - the Russian oligarch at the centre of a multi-billion dollar legal battle with Roman Abramovich - during the graveside ceremony this morning.
A fleet of black limousines arrived at Highgate cemetery in north London as around 10 close family friends paid tributes and delivered short speeches in Russian and English. Flowers were also placed near a new gravestone recently erected in his memory.
Mr Litvinenko, 43, fell ill shortly after drinking tea during a meeting at a West End hotel with Lugovoy and Kovtun.
Three weeks later, on November 23, 2006, he died of radioactive polonium-210 poisoning in London's University College Hospital.
British prosecutors named Lugovoy as the main suspect in the dissident's killing, but the Russian authorities have repeatedly refused to send him to the UK.