BRUSSELS - NATO’s secretive Nuclear Planning Group met Thursday as the military alliance presses ahead with plans to hold a nuclear exercise next week as concerns deepen over President Vladimir Putin’s insistence that he will use any means necessary to defend Russian territory.

Defense ministers led the session, which usually happens once or twice a year, at NATO headquarters in Brussels. It comes against a backdrop of high tension as some NATO allies, led by the U.S., supply Ukraine with advanced weapons and munitions to defend itself against Russian aerial attacks.

NATO is keeping a wary eye on Russia’s movements, but has so far seen no change in its nuclear posture.

But additional uncertainty comes from the fact that Russia is also due to hold its own nuclear exercises soon, possibly at the same time as NATO or just after, according to NATO diplomats. That could complicate the 30-country military organization’s reading of the war and of Moscow’s intentions.

“Russia will also be conducting its annual exercise, I think, the week after or just after the annual exercise,” U.K. Defence Secretary Ben Wallace told reporters. But “what we don’t want is to do things out of routine.”

“This is a routine exercise and it’s all about readiness,” Wallace said, just as “NATO’s meeting is all about making sure we are ready for anything. I mean, that is the job of this alliance — to make sure that the 30 partners together are ready for what is thrown at us. And we have to continue to work at that.”

NATO’s exercise, dubbed “Steadfast Noon,” is held around the same time every year and runs for about one week. It involves fighter jets capable of carrying nuclear warheads, but doesn’t involve any live bombs. Conventional jets, and surveillance and refueling aircraft also routinely take part.

Fourteen NATO member countries will be involved in the exercise, which was planned before Russia invaded Ukraine on Feb. 24. The main part of the maneuvers will be held more than 1,000 kilometers (625 miles) from Russia.

NATO as an organization doesn’t possess any weapons. The nuclear weapons nominally linked to the alliance remain under the firm control of three member countries — the U.S., the U.K. and France. But France insists on maintaining its nuclear independence and doesn’t take part in Nuclear Planning Group meetings.

With the Russian army retreating under the blows of Ukrainian forces armed with Western weapons, Putin raised the stakes by annexing four Ukrainian regions and declaring a partial mobilization of up to 300,000 reservists to buttress the crumbling front line.

As his war plans have gone awry, Putin has repeatedly signaled that he could resort to nuclear weapons to protect the Russian gains. The threat is also aimed at deterring NATO nations from sending more sophisticated weapons to Ukraine.

In an interview with France 2 television on Wednesday, French President Emmanuel Macron warned about the responsibilities of leaders when it comes to nuclear rhetoric. He said he has spoken to Putin “several times.”

“We have a (nuclear) doctrine which is clear,” Macron said. “The dissuasion is working. But then, the less we talk about it, the less we brandish the threat, the more credible we are.”

“Too many people are talking about it,” he said.

Earlier this week, NATO Secretary-General Jens Stoltenberg described Putin’s remarks as “dangerous and reckless,” and underlined that the allies “have also conveyed clearly to Russia that it will have severe consequences if they use nuclear weapons in any way.”

Stoltenberg warned that it “would be absolutely the wrong signal to send” if the world’s biggest security organization were to cancel the maneuvers.

“NATO’s firm, predictable behavior, our military strength, is the best way to prevent escalation,” he said. “If we now created the grounds for any misunderstandings, miscalculations in Moscow about our willingness to protect and defend all allies, we would increase the risk of escalation.”