No one can win from a nuclear war and it should "never be unleashed", Vladimir Putin has warned.

The Russian president warned on Monday that there could be "no winners" if such a conflict was to break out. He made the statement as a review of a keystone nuclear treaty opened at the United Nations.

Mr Putin insisted that Moscow had "consistently" remained faithful to the Non Proliferation Treaty's (NPT) "letter and spirit" in his address to the Tenth NPT Review Conference.

It marked a change of tone from the start of his invasion of Ukraine, when the strongman leader made thinly veiled threats hinting at a willingness to deploy Russia's tactical nuclear weapons, which according to Russian military doctrine can be used to force an adversary to retreat.

The US, Britain and France had rebuked Russia for "irresponsible and dangerous" talk about possibly deploying nuclear weapons. Ties between Russia and the West have been unravelling over the course of the conflict, now five months in.

Opening the conference in New York, UN secretary general Antonio Guterres warned that the world now faces a "nuclear danger not seen since the height of the Cold War".

“Humanity is just one miscalculation away from nuclear annihilation," he said. Citing Russia’s war in Ukraine and tensions on the Korean peninsula and in the Middle East, he called the conference "a chance to strengthen" the treaty and "make it fit for the worrying world around us”.