The British government's emergency planning committee, COBRA, has been meeting again to assess progress in the investigation into the death of the former Russian spy, Alexander Litvinenko.
Earlier, the Russian president, Vladimir Putin, said the death in London of the ex-spy is being used as a 'political provocation' against Russia.
Mr Litvinenko's death has been linked to the presence of a major dose of radioactive polonium-210 in his body.
British authorities have launched an intensive investigation, and in the latest development, the Russian ambassador in London has been asked to provide more information on Mr Litvinenko's death.
Mr Litvinenko was a fierce critic of the Russian president.
Speaking before British police said they had found radioactive material in his body, Mr Putin said there was no evidence Mr Litvinenko's death had been unnatural.
