WASHINGTON

The US has seen "no indication" that Russian President Vladimir Putin has chosen to use nuclear weapons or other weapons of mass destruction in Ukraine, the White House said on Tuesday. 

National Security Council spokesman John Kirby said that despite Putin's saber rattling, the US has not detected any signs that the Kremlin is moving forward with any preparations "for that kind of decision."

"We certainly have seen nothing that would cause us to change our own strategic deterrent posture in any way when it comes to our own ability to defend ourselves and our allies and partners," Kirby told reporters. "Nobody wants to see this war escalate into the nuclear realm."

Earlier on Tuesday, Russian Foreign Minister Sergey Lavrov said the Kremlin's military doctrine allows only for the defensive use of nuclear weapons.

"I hope that those who constantly speculate on the issue of a nuclear war ... are aware of their responsibility," he said during a television interview.

"I am appealing to all those that are interested in this situation and trying to cover it in the public space to refrain from artificially warming it up," the top diplomat said.

Putin, however, raised the specter of nuclear war as he prepared to hold votes in occupied Ukrainian regions that he and allies used as a pretext to annex additional territories.

"When the territorial integrity of our country is threatened, we will certainly use all the means at our disposal to protect Russia and our people. This is not a bluff," Putin said just days before he moved to claim four Ukrainian regions as Russian territory.