President Vladimir Putin warned the West on Wednesday that Russia could use nuclear weapons if it was struck with conventional missiles, and that Moscow would consider any assault on it supported by a nuclear power to be a joint attack.

The decision to change Russia's official nuclear doctrine is the Kremlin's answer to deliberations in the United States and Britain about whether to give Ukraine permission to fire conventional Western missiles into Russia.

Putin, opening a meeting of Russia's Security Council, said that the changes were in response to a swiftly changing global landscape that had thrown up new threats and risks for Russia.