STORY: NATO on Sunday criticized Vladimir Putin for what it called his "dangerous and irresponsible" nuclear rhetoric.
This comes after the Russian president said Saturday he would station tactical nuclear weapons in Belarus, Ukraine's neighbor.
Putin likened it to the U.S. stationing its weapons in Europe, while insisting that Russia would not violate its nuclear non-proliferation promises.
A NATO spokesperson said in emailed comments to Reuters on Sunday that "Russia has consistently broken its arms control commitments."
It's one of Russia's most pronounced nuclear signals since the beginning of its invasion of Ukraine 13 months ago.
And Ukraine's foreign ministry on Sunday called for an extraordinary meeting of the UN Security Council and for the international community to "take decisive measures" to prevent Russia's use of nuclear weapons.
Washington played down concerns -- White House National Security Council spokesman John Kirby said the U.S. had seen no sign that Putin had moved any nuclear weapons.
Meanwhile, Ukrainian forces have managed to blunt Russia's offensive in and around the embattled eastern city of Bakhmut, the scene of brutal fighting in the last few months.
Ukraine's General Staff said on Sunday that Ukrainian forces had repelled 85 Russian attacks over the past 24 hours in several parts of the eastern front, including Bakhmut.
Separately, Britain's defense ministry said the months-long Russian assault on the city had stalled, mainly as a result of heavy troop losses.
Reuters could not immediately verify the battlefield reports.