Former Russian spy Alexander Litvinenko has reportedly died in hospital after being poisoned. Sky News sources have learned that the ex-KGB agent has died after his condition had been deteriorating throughout the day.
Mr Litvinenko's supporters have accused the Russian government of poisoning the 43-year-old, who had been given asylum and citizenship in Britain after fleeing Russia.
They said he was killed because he was investigating the murder last month of journalist Anna Politkovskaya, who was shot dead near her Moscow apartment.
The Kremlin has said the accusation is "sheer nonsense".
Mr Litvinenko fell ill after meeting a contact, an Italian journalist, in a sushi restaurant in central London.
Dramatic photographs released this week showed him lying in intensive care. His hair had fallen out and his complexion was jaundiced.
Last night he suffered a heart attack and doctors said his condition had worsened. Friends and relatives were said to be rushing to his bedside fearing the worst.
Doctors still do not know what caused his illness, although they have said he was poisoned.
Initial reports suggested he had been poisoned with thallium, or with a radioactive material, but doctors have now said this was not the case.
Professor Mario Scaramella, the Italian who met Mr Litvinenko for lunch before he fell ill, said he had shown him documents suggesting that both men were on a hit-list.
Mr Litvinenko, an outspoken critic of President Vladimir Putin, was probing the murder of Ms Politkovskaya, who had become famous for exposing Russian atrocities in Chechnya.
Thirteen journalists have been murdered in Russia since Mr Putin came to power in 2000. None of the cases has been solved.
