The exercise, dubbed "Steadfast Noon," is held annually and usually runs for about one week. It involves fighter jets capable of carrying nuclear warheads but does not involve any live bombs. Conventional jets, and surveillance and refuelling aircraft also routinely take part.

The main part of the manoeuvres would be held more than 1,000 kilometers from Russia, a NATO official said.

NATO will push ahead with long-planned nuclear exercises next week despite rising tensions over the war in Ukraine and President Vladimir Putin's insistence that he is not bluffing about using all available means to defend Russian territory, NATO Secretary-General Jens Stoltenberg said Tuesday. The exercise, dubbed "Steadfast Noon," is held annually and usually runs for about one week.

It involves fighter jets capable of carrying nuclear warheads but does not involve any live bombs. Conventional jets, and surveillance and refuelling aircraft also routinely take part.

Fourteen of the 30 NATO member countries will be involved in the exercise, which was planned before Russia invaded Ukraine in February.

The main part of the manoeuvres would be held more than 1,000 kilometers from Russia, a NATO official said.

"It would send a very wrong signal if we suddenly now cancelled a routine, long-time planned exercise because of the war in Ukraine. That would be absolutely the wrong signal to send," Stoltenberg told reporters on the eve of a meeting of NATO defence ministers in Brussels.

"NATO's firm, predictable behaviour, 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."

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 mobilisation of up to 300,000 reservists to buttress the crumbling front line.

As his war plans have gone awry, Putin has repeatedly signalled 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.

NATO as an organisation does not possess any weapons. The nuclear weapons nominally linked to NATO remain under the firm control of three member countries - the U.S., U.K. and France. The alliance's secretive Nuclear Planning Group will meet on Thursday among defence ministers.

Stoltenberg described Putin's spiralling nuclear rhetoric 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."

"We are closely monitoring Russia's nuclear forces," Stoltenberg said. "We have not seen any changes in Russia's posture, but we remain vigilant."