Britain has broadened the investigation into the death of former Russian spy Alexander Litvinenko after police discovered the radiation that killed him in additional locations.

British Home Secretary John Reid Monday said that investigators have confirmed the discovery of traces of the isotope, Polonium 210, in "several other premises" that Litvinenko visited before he fell ill. Mr. Reid did not identify the premises.

Britain has asked Russia for a full cooperation in the probe. The former Russian spy, who wrote a book slamming the Russian security service, said that his poisoning was ordered by Moscow.

Litvinenko's death comes just weeks after the assassination of journalist Anna Politkovskaya, who was critical of President Putin's crackdown on Chechnya.

Two journalists who worked with Politkovskaya received death threats Friday after writing articles questioning a problem in the North Caucasus and the investigation into their colleague's murder.

Russian government denies involvement in the deaths.

Some information for this report was provided by AFP, AP and Reuters.