Vladimir Putin, the Russian president, yesterday personally signed a law suspending Russia's participation in a key post-cold war arms treaty, in a move that will effectively kill off one of the landmark defence agreements between Moscow and the west.

In a significant sign of the worsening diplomatic relationship between Moscow and Washington, Mr Putin made a point of being seen to approve the decision to walk away from the Conventional Forces in Europe treaty in a little under two weeks' time. His decision triggered an angry reaction from the US, which declared the "unilateral" move to be a "mistake."