Russia would use its nuclear weapons in response to an incoming missile attack, Vladimir Putin has said.
The Russian president said the country would only launch a nuclear strike if its early warning systems spot missiles heading toward its territory.
“The aggressor should know that retaliation is inevitable,” he told an international policy forum in Sochi.
“When we see a coming strike on the territory of Russia, we will retaliate.”
Mr Putin acknowledged it would mean a global catastrophe, but emphasised Russia “can’t be those who initiated it”.
“We would be victims of aggression and would get to Heavens as martyrs,” he said, adding those who would launch the strike would “just die and not even have time to repent.”
In March, Mr Putin unveiled what he said was a new arsenal of advanced weaponry including nuclear devices immune to enemy interception.
Two of the weapons were a nuclear-powered cruise missile and an artificial drone, he said.
Mr Putin said the missile, which was tested late last year, had an unlimited range and could penetrate any missile defence.
The drone can carry a nuclear warhead and target both aircraft carriers and coastal facilities, according to the Russian president.
Mr Putin said the weapons made NATO’s US-led missile defence system “useless” and signalled the end to Western efforts to check Russia’s nuclear ambitions.
He added that the development of the new weapons was in response to the US withdrawing from a Cold War-era treaty that banned missile defences and Washington’s moves to develop a missile defence system.