Russian President Vladimir Putin has said the threat of a nuclear war was rising but insisted Moscow had not "gone mad" and would not use its nuclear weapons first.

Speaking at Russia's annual human rights council meeting, he also said the war in Ukraine could be a "lengthy process", the BBC reported.

"Such a threat is growing, it would be wrong to hide it," Putin warned while talking about the prospect of nuclear war via video link from Moscow.

But he asserted that Russia would "under no circumstances" use the weapons first, and would not threaten anyone with its nuclear arsenal.

"We have not gone mad, we are aware of what nuclear weapons are," he said, adding: "We aren't about to run around the world brandishing this weapon like a razor."

The President also boasted that Russia had the most modern and advanced nuclear weapons in the world, and contrasted its nuclear strategy to the US, who he said had gone further than Russia by locating its nuclear weapons on other territories, the BBC reported.

"We do not have nuclear weapons, including tactical ones, on the territory of other countries, but the Americans do, in Turkey, and several other European countries," he said.

Putin has previously insisted that Russia's nuclear doctrine only allowed for the defensive use of nuclear arms. (KB/IANS)