REUTERS

A Downing Street aide told the paper the report would blame the Kremlin for the killing, but added 'we won't be declaring war on Russia', according to the report.

Intelligence sources told the paper there was no 'smoking gun' pointing to the Russian leadership, but there was 'no doubt' about the people who were physically responsible'.

Read alsoThe Guardian: How UK scientists solved Alexander Litvinenko riddleLitvinenko, a Russian dissident and fierce critic of Putin, was given a lethal dose of polonium in a cup of green tea during a meeting at the Millennium Hotel in Mayfair in November 2006. It took him three weeks to die.

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