LONDON (AFP) -- British detectives believe that the radioactive substance used to kill former Russian spy Alexander Litvinenko cost in excess of 10 million dollars (7.6 million euros), The Times reported in an early edition of its Monday newspaper.

According to the newspaper, preliminary results from the post-mortem on Litvinenko's body have shown that he was given more than ten times the lethal dose of polonium-210, large quantities of which were found in his urine.

Litvinenko, 43, fell ill on November 1 and died on November 23. Several of his friends have blamed the Kremlin for the murder, but Russia has repeatedly denied that it had any involvement in the ex-spy's death.

United Nuclear Scientific Supplies, based in New Mexico and one of the few companies allowed to sell polonium-210 over the Internet, told The Times that it would take at least 15,000 units of the isotope to kill someone.

With each unit costing 69 dollars, that would mean that it would cost more than 10 million dollars to deliver the fatal dose, the newspaper said.

The Times also said that British detectives currently in Moscow continuing their investigation are due to return to Britain in the coming week.