
A spokesman for London's University College Hospital said Mr Litvinenko died at 9.21pm. He said the medical team at the hospital did everything possible to save his life.
The spokesman added: "Every avenue was explored to establish the cause of his condition and the matter is now an ongoing investigation being dealt with by detectives from New Scotland Yard.
"Because of this we will not be commenting any further on this matter. Our thoughts are with Mr Litvinenko's family."
A Scotland Yard spokesman said inquiries were continuing.
"Although formal identification has not taken place at this stage, we are satisfied that the deceased is Mr Litvinenko and the matter is being investigated as an unexplained death," the police spokesman said.
Police investigating how he became ill and have previously said that they suspected deliberate poisoning.
Investigators are working through potential toxins to see what might have caused Mr Litvinenko's condition.
Mr Litvinenko, a defector to Britain who was granted asylum and citizenship, is thought to have been poisoned on November 1. He had been investigating the murder of an American female journalist in Moscow.
In his final interview, just hours before he fell unconscious, the former intelligence officer remained defiant against the people he believed had poisoned him.
"I want to survive, just to show them," he told filmmaker and friend Andrei Nekrasov.
Mr Nekrasov told the Times that Mr Litvinenko had said: "The bastards got me but they won't get everybody," The Guardian reported.
Russian Defector Converted To Islam Before His Death?
Alexander Litvinenko who was poisoned in London by the FSB, a Russian secret service, for criticizing Putin and died from poisoning on Thursday night, November 23, 2004, converted to Islam some time ago, the Chechenpress news agency reported.
Before he died, Muslim rituals were perforned at his death bed. A mullah, invited from a London mosque, read the Sunnah Yasin.
KC