STORY: He spoke at a news conference held at NATO headquarters in Brussels after Russian President Vladimir Putin delivered a warning to the West over the war in Ukraine and announced its decision on the New START treaty.

The treaty between Moscow and Washington, signed in 2010, limits the number of atomic warheads the world's two biggest nuclear powers can deploy and is due to expire in 2026.

Replying to Putin's accusations that the West was trying to destroy Russia, Stoltenberg said Moscow was the aggressor in Ukraine where it launched a invasion almost a year ago.