He voiced confidence that Russia could resist Western pressure and expressed hope that U.S. President Donald Trump eventually would move to repair fractured ties with Russia.
Speaking at an international policy forum in Sochi, Putin noted that Russia's military doctrine doesn't envisage a preventative nuclear strike. He said Moscow only would tap its nuclear arsenal if early warning systems spotted missiles heading toward Russia.
"Only when we become convinced that there is an incoming attack on the territory of Russia, and that happens within seconds, only after that we would launch a retaliatory strike," he said during a panel discussion at the forum.
"It would naturally mean a global catastrophe, but I want to emphasize that we can't be those who initiate it because we don't foresee a preventive strike," Putin said. "The aggressor should know that retaliation is inevitable, and he will be destroyed."
"We would be victims of an aggression and would get to heaven as martyrs," while those who initiated the aggression would "just die and not even have time to repent," he added.
The Russian leader also warned that new hypersonic missiles his country developed give it a military edge.
"We have run ahead of the competition. No one has precision hypersonic weapons," he said. "Others are planning to start testing them within the next 1½ to 2 years, and we already have them on duty."
Russia already has deployed the Kinzhal hypersonic missile. Putin said that another new weapon, the Avangard, is set to enter service in the next few months.
Earlier this year, Putin said the Avangard has an intercontinental range and can fly in the atmosphere at a speed 20 times the speed of sound, making it capable of piercing any missile defense system.
His blunt talk Thursday comes as Russia-West relations remain frosty over the Ukrainian crisis, the war in Syria and the allegations of Russian meddling in the 2016 U.S. presidential vote.
Putin said he still hoped Trump would be able to improve the ties between their countries. He thinks Trump wants "some sort of stabilization and improvement of U.S.-Russian ties" and said Moscow is ready for that "at any moment."
Putin said his meeting with Trump in Helsinki in July was positive and they had a "normal, professional dialogue" even though their exchange brought strong criticism for Trump. He dismissed the dynamic as the result of "the internal political struggle."
"Some people think that playing the Russian card is a very convenient instrument for solving internal political problems," Putin said. "I hope it will go away. I don't know if it happens after the congressional elections, but it might. Or it may happen after the 2020 U.S. presidential election, when he will no longer have to constantly look back at those who engage in anti-Russian rhetoric."
At the same time, the Russian president sharply criticized Washington's reliance on sanctions against Russia and others, saying the instrument of punishment "undermines trust in the dollar as a universal payment instrument and the main reserve currency."
"It's a typical mistake made by an empire," Putin said. "An empire always thinks that it's so powerful that it can afford some mistakes and extra costs. But mistakes and costs multiply, and a moment comes when they become overwhelming in both security and economic spheres."
Building on his defiance and boasts, Putin said Russia had nothing to fear given its resources, defense capability and "people ready to defend our sovereignty and independence."
"Not in every country are people so eager to sacrifice their lives for the Motherland," he said.
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