The United States on Wednesday denounced "loose talk" on nuclear weapons after Russian President Vladimir Putin mused on rising risks of nuclear war but said Moscow would not strike first.
Putin, who has previously hinted at use of small "tactical" weapons in his war in Ukraine, said at a Kremlin meeting that "such a threat is rising" but he was evasive on Russia's policy.
"Russia will under no circumstances use them first," Putin said.
"But if it does not use them first under any circumstances, then it will not be the second to use them either, because the possibilities of using them in the event of a nuclear strike against our territory are very limited," Putin said.
US State Department spokesman Ned Price, asked about Putin's remarks, declined to reply directly but said, "We think any loose talk of nuclear weapons is absolutely irresponsible."
Price said that nuclear powers around the world since the Cold War, including China, India, the United States and Russia itself, have been clear that "a nuclear war is something that must never be fought and can never be won."
"We think any other rhetoric -- whether it is nuclear saber-rattling or even raising the specter of the use of tactical nuclear weapons -- is something that is irresponsible," Price said.
"It is dangerous, and it goes against the spirit of that statement that has been at the core of the nuclear non-proliferation regime since the Cold War," he said.
Putin in his remarks contrasted Russia with the United States, pointing to Washington's stationing of nuclear weapons in NATO allies in Europe.
"We have not, and are not, transferring our nuclear weapons to anyone, but, of course, we will protect our allies with all the means at our disposal, if necessary," Putin said.
US officials have voiced fear that Russia could use nuclear weapons if it feels routed on the battlefield and could plant a fictitious story to justify its actions.
Russia has already spoken of supposed Ukrainian attempts to detonate a "dirty bomb," drawing strong denials from Ukraine and a sharp rebuke from the United States, which had rare direct communication with Moscow to warn against nuclear use.
Neither the United States nor Russia -- by far the largest nuclear weapons powers -- officially has a policy of no first use of the ultra-destructive arms.
A recent US posture review by President Joe Biden concluded only that nuclear weapons should only be used in "extreme circumstances."
Russia recently cancelled talks on nuclear arms control scheduled in Cairo, accusing the United States -- which has sought to punish Russia over its invasion of Ukraine -- of hostility.