REUTERS, Moscow

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 or not 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 which had thrown up new threats and risks for Russia.

The 71-year-old Kremlin chief said he wanted to underscore one key change in particular.

“It is proposed that aggression against Russia by any non-nuclear state, but with the participation or support of a nuclear state, be considered as their joint attack on the Russian Federation,” Putin said.