Mark Rutte said an annual nuclear exercise by NATO member states, which starts next week, sends a clear message to adversaries "that we stand ready to… respond to any threat".

The former Dutch prime minister also spoke about Russia's war in Ukraine.

He said he doubted Ukraine is weaker because it has yet to be given permission by the UK and other allies to use long-range weapons to strike targets inside Russia, signalling that - provided the West continues to support Kyiv - "one weapons system will not change the outcome of the war".

Mr Rutte, who took over as secretary general of NATO at the start of the month from Jens Stoltenberg, held a meeting in Downing Street with Sir Keir Starmer on Thursday.

He also took part in a three-way discussion with Volodymyr Zelenskyy, who was similarly paying the British prime minister a visit.

The Ukrainian leader is on a quick tour of European capitals armed with what Ukraine is calling a "victory plan" to end Russia's invasion.

Mr Rutte, who sat down for an interview after the meetings, declined to divulge details about the Ukrainian plan but said he hopes victory comes "as soon as possible".

He also said it is vital to keep supporting Kyiv with weapons, training and funding so that Mr Zelenskyy is in the strongest possible position for any future talks.

Asked if Ukraine is weaker because allies such as the UK and the US have yet to grant permission for Kyiv to use their long-range weapons, such as British Storm Shadow cruise missiles, against targets inside Russia, the NATO chief said: "I'm not sure it is."

He continued: "There is this risk that we completely focus on one weapon system and then that is the thing of the day… to be absolutely clear, the main issue here is making sure that military aid continues to flow into Ukraine, that we ramp up also the industry production within Ukraine, help them with that massive logistics, and then one weapon system will not change the outcome of the war."

Russian President Vladimir Putin has warned that he would regard the use by Ukraine of western long-range missiles inside Russia as NATO states directly participating in the war.

"It would substantially change the very essence, the nature of the conflict," he said last month.

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Mr Rutte was blunt when quizzed whether NATO allies should heed Russian sabre rattling.

"No, they shouldn't, and they don't," he said.

He continued: "NATO is strong. We can face any adversary. We have everything in place to make sure that NATO is safe and secure, and that we can fight off any threat. And we will never be intimidated by anyone outside NATO trying to threaten us. So that is of no use he could better stop that."

Against the backdrop of increased Russian nuclear weapons threats over Ukraine, NATO is due to begin its yearly Steadfast Noon nuclear exercise next week.

It will be led by Belgium and the Netherlands, use eight military bases and involve 2,000 personnel and 60 aircraft from 13 nations.

Bomber aircraft and fighter jets that can carry nuclear warheads are taking part. No live munitions are used.

Asked what message he hoped the exercise would send to the Kremlin, Mr Rutte said: "It is crucial that we test and strengthen our defence.

"We also clearly sent a message to our adversaries that we stand ready to… respond to any threat."