NATO Secretary-General Jens Stoltenberg on Thursday said the circumstances in which the military alliance would resort to using nuclear weapons over Russia's war in Ukraine were "extremely remote."

Stoltenberg was speaking at the close of two-day meeting of NATO defense ministers in Brussels, including closed-door discussions by its Nuclear Planning Group.

The meeting came as Russian leader Vladimir Putin regularly threatens the use of nuclear weapons as he faces losses on the battlefield in Ukraine.

What NATO and Russia said about nuclear weapons

Stoltenberg told journalists that Moscow's nuclear rhetoric "is dangerous, reckless."

"They know that if they use a nuclear weapon against Ukraine it will have severe consequences, and they also know that a nuclear war cannot be won and should never be fought," Stoltenberg said, without specifying what a response would involve.

He said the use of a nuclear weapon would "fundamentally change the nature of the war in Ukraine" and will mean "a very important line has been crossed."

Ahead of the meeting, US Defense Secretary Lloyd Austin reaffirmed Washington's commitment to defending "every inch" of NATO territory.

Alexander Venediktov, the deputy secretary of Russia's Security Council, reissued nuclear warnings again Thursday. 

He was quoted in Russian state media as saying: "Kyiv is well aware that such a step," as Ukraine joining NATO, "would mean a guaranteed escalation to World War Three," calling it "suicidal" for existing NATO member states.

Steadfast Noon annual exercise

The meeting of NATO defense ministers also came ahead of the alliance's annual Steadfast Noon exercise.

The exercise, scheduled for next week, will play out how a nuclear scenario would be handled by the alliance's members.

Held annually around the same time of year, Steadfast Noon involves fighter jets, conventional jets, refueling and surveillance aircraft.

No nuclear weapons are involved. Members will drill for the successful deployment of a US nuclear weapon based in Europe.

Stoltenberg said at Thursday's press conference that the annual exercise was planned long before Russia's invasion of Ukraine. He said the drill aimed "to ensure our nuclear deterrence is safe, secure and effective ... deterrence is the way to prevent any attack on a NATO ally and to preserve peace."

Earlier this week, Stoltenberg said canceling Steadfast Noon at this moment "would be absolutely the wrong signal to send" as Putin's nuclear rhetoric is "dangerous and reckless."

Fourteen allied nations are scheduled to take part in the exercises, which were planned well in advance of Russia's invasion of Ukraine. The biggest part of the exercise will take place more than 1,000 kilometers (625 miles) from Russia.

Russia is also scheduled to hold nuclear exercises in the near future, possibly at the same time as NATO exercises or soon after, NATO diplomats told The Associated Press news agency.

What nuclear weapons are in NATO's arsenal?

NATO as a military organization does not possess a nuclear arsenal, rather member states do, just as NATO forces are comprised of member states' forces.

In NATO, only three members possess nuclear weapons: the US, the UK and France, all permanent members of the UN Security Council.

France, however, does not participate in the Nuclear Planning Group due to its insistence on "strategic autonomy," or independence as it was known before French President Emmanuel Macron used the term.

"We do not want a World War," Macron tweeted.

ar,nm/fb (AP, Reuters)