Stoltenberg mounted a vigorous defence of NATO ahead of a meeting of alliance foreign ministers, saying it was doing more than ever and warning against undermining it.

The diplomatic shockwaves from Macron's forthright interview with The Economist continue to rattle NATO just weeks before a summit in London meant as a 70th birthday celebration for the alliance.

"I will go to Paris next week and there I intend to discuss these issues with President Macron -- I think that's the best way to address any differences, to sit down and discuss them and to fully understand the messages and the motivations," Stoltenberg told reporters.

"My message is that NATO is adapting, NATO is agile, NATO is responding."

Macron said he believed the alliance was undergoing "brain death", decrying what he called a lack of strategic coordination between Europe and the United States and lamenting NATO member Turkey's recent unilateral military incursion in Syria.

While French officials have argued that Macron was simply stating difficult truths that other allies preferred to ignore, there has been little public sympathy for his remarks -- other than from the Kremlin, which welcomed them warmly.

German Chancellor Angela Merkel condemned Macron's "sweeping judgements", insisting that NATO remained indispensible for European security.

Several NATO members in eastern Europe -- where concerns about Russia run high, fuelled by memories of Soviet domination -- were horrified at the Macron interview, in which he also called for moves towards rapprochement with Moscow.

The US ambassador to NATO, Kay Bailey Hutchison, said Washington "firmly disagreed" with Macron's assessment of NATO and with his call for Europe to be able to ensure its own defence without US support.

"The thought of only one of our countries or one of our groups of countries facing the enormous risks to our population alone is not even rational. We are stronger together," she said.

The row over Macron's comments adds to the clouds looming over the December 3-4 gathering of NATO leaders in London.

Organisers will be hoping for a less mercurial performance from US President Donald Trump than at the summit in Brussels last year where he caused consternation with his vehement criticism of defence spending by Europe -- and Germany in particular.

The London meeting also comes with tensions running high with Turkey -- both over its operation in Syria and increasing closeness to Moscow, manifested most dramatically in Ankara's purchase of Russia's S-400 anti-aircraft missiles.