The report itself -- covering expenditures before Russia launched its war in February this year -- showed just eight of NATO's 30 member nations were meeting a target of spending two percent of GDP on defence.

As usual, the United States -- by far the biggest military power in NATO -- led spending, with 3.6 percent, around the same level as Greece.

The other six countries to exceed the two-percent "guideline" were: Poland, Britain, Croatia, Estonia, Latvia and Lithuania.

That was a smaller cohort than in 2020, when 11 NATO countries met the two percent target.

But Stoltenberg said the war in Ukraine had brought "a new security reality" and allies were stepping up to it.

He pointed to the announcement by Germany just days after the February 24 invasion that it was going to plough 100 billion euros ($110 billion) into its dilapidated military and surpass the two-percent defence spending goal.

He also highlighted similar pledges by Denmark, Poland and Romania to meet the target.

"Together, this makes a huge difference," he said.

Stoltenberg acknowledged that governments had to juggle spending priorities between defence, health, education and infrastructure.

But, he said: "At the same time when we see a new security reality, when we see the aggressive actions of Russia against Ukraine, then we all realise the need to invest in our security."

Stoltenberg said the upped spending pledges would inform a Madrid summit of NATO leaders in June, which is to chart out a new defence posture for the alliance, especially geared to the demonstrated threat from Russia.

"I think what you're seeing is that there's a need to invest more in air defence, there's a need to invest more in higher readiness, to also have more ammunition, more and more ability to sustain operations for a longer period of time, and high-end capabilities," he said.