The state-sponsored assassination of Russian dissident Alexander Litvinenko was a "blatant and unacceptable" breach of international law, Theresa May has told MPs.
President Vladimir Putin "probably" approved the assassination of the former spy in London in 2006, a public inquiry has found.
In a dramatic conclusion, Sir Robert Owen said it was likely that the Russian leader signed off the killing of Mr Litvinenko following a long-running feud.
The Home Secretary told the Commons that the two men responsible - Andrei Lugovoi and Dmitri Kovtun - would have their assets frozen and the Russian ambassador was being summoned.
MPs were told that the Government remains committed to bringing his killers to justice.
Mrs May said: "This was a blatant and unacceptable breach of the most fundamental tenets of international law and civilised behaviour. But we have to accept that this doesn't come as a surprise."