In an interview with The Telegraph, the 63-year-old says he is preparing for that “reinforcement” to be turned into a fundamental “reset” of the alliance, which was born out of the 1949 North Atlantic Treaty between the US, Canada and European nations. He has agreed to extend his second term for another year to oversee the transformation.

That reset, he says, must be accompanied by increased national defence spending by Nato members, many of whom still allocate less than the alliance’s minimum threshold of 2 per cent expenditure as a share of their GDP.

In the UK, where Rishi Sunak, the Chancellor, is facing pressure to increase military spending above the current level of about 2.2 per cent, a rise would also be welcome, Mr Stoltenberg says.

“The 2 per cent guideline is a minimum guideline and of course I welcome every increase in defence spending from all allies – also, of course, those allies who are already spending more than 2 per cent, like the United Kingdom.

“But of course my main focus is to ensure that those that are below 2 per cent meet that minimum guideline.”

Speaking at Nato headquarters in Brussels, Mr Stoltenberg singles out Olaf Scholz, the German chancellor, for committing to a sharp increase in Berlin’s spending on defence, from about 1.5 per cent of GDP to more than 2 per cent.

“With the size of the German economy, this really makes a huge difference also for Nato’s total defence spending,” he says.

Mr Stoltenberg also praises the UK’s role in helping Ukraine defend itself against Russia.

In the years prior to the invasion, he says, tens of thousands of Ukrainian troops benefited from training and equipment provided by the UK and other Nato allies, making the country’s armed forces “much bigger, much better equipped, much better trained, and much better led now than ever before.

“And after the invasion, allies stepped up, and the United Kingdom is playing a key role, both in providing training over many years, but also in stepping up their efforts to provide more support now.”