A highly radioactive material called Polonium 210 has been found in the body of dead ex-Russian spy Alexander Litvinenko, Sky sources say.

It came as Home Secretary John Reid revealed the police were searching for residual radioactive material at a number of locations, including Mr Litvinenko's house in north London.

They want to find out who killed the 43-year-old former security agent and how he was poisoned.

Before he died in a London hospital on Thursday night, Mr Litvinenko wrote a statement which blamed Russian President Vladimir Putin for ordering his murder.

Poisoned: Alexander Litvinenko

Friends said the statement was penned on Tuesday, when Mr Litvinenko realised he was dying.

He accused the Russian leader of having "no respect for life, liberty or any civilised value".

He told Mr Putin: "You have shown yourself to be unworthy of your office, to be unworthy of the trust of civilised men and women."

The Russian leader said the death was a tragedy, but he had not seen any definitive proof that it was a "violent death". He also brushed off suggestions linking him to the case.

Mr Litvinenko's tearful father Walter said: "This (Russian) regime is a mortal danger to the world."

He added: "It was an excruciating death, he was taking it as a real man. Even before his death, in such a state he never lost his human dignity."

The ex-spy fell ill after meeting a contact, an Italian journalist, in a sushi restaurant in central London.

It is still not clear what type of substance was used. Thallium had been suggested, but this now appears to have been ruled out.

Mr Litvinenko's supporters said he was killed because he was investigating the murder last month of journalist Anna Politkovskaya.

Like Mr Litvinenko himself, she was a fierce critic of Mr Putin but the Kremlin said the accusation was "sheer nonsense".

Source: Sky News