Britain's Home Secretary John Reid says traces of radiation have been found in a dozen U.K. sites during the ongoing investigation into the London death of former Russian spy Alexander Litvinenko.
Earlier it was reported that "very low traces" of radiation were found on two British Airways planes that had recently made trips to Moscow. Authorities are now interested in examining three additional planes.
Litvinenko was an outspoken critic of the Russian government, and reportedly blamed his poisoning on the Kremlin before his death. The Russian government has denied any involvement in the former spy's demise.