"There can be two reasons that can make us use nuclear weapons: an attack against us with nuclear weapons or an attack on Russia with conventional weapons. But the second case is only if it threatens the existence of the Russian state," Vladimir Putin said.
Putin said he had offered to collaborate on the joint improvement of missile defenses with the United States but had been rebuffed, so he had to act in Russia's best interests.
"Instead of creating threats to one another, great powers should join their efforts in protecting against terrorists," he said.
Commenting on suggestions that Russia could spark a new Cold War, Putin emphasized, "the individuals that have said that a new Cold War has started are not analysts. They do propaganda."
On Thursday, Putin made his annual address to the country's bicameral parliament, the Federal Assembly, which comprises the Federation Council and State Duma. The Russian leader announced his country's development of new types of armaments, including intercontinental underwater drones, nuclear-powered cruise missiles, and a prospective hypersonic missile, and showed footage featuring tests of these weapons.
The Russian president stressed that Russia's efforts toward enhancing its defense capabilities were being carried out within the framework of existing international accords. According to Putin, Russia is creating advanced weapon systems in response to the deployment of US missile defense systems, and these arms present no threat to other states.