In an interview with British weekly The Economist, Emmanuel Macron expressed doubt about U.S.-led NATO's security maxim that an attack on one ally is an attack on all, which has underpinned transatlantic ties since the alliance's 1949 foundation.
"What we are currently experiencing is the brain death of NATO," Macron said. Asked whether he still believed in the Article Five collective defense guarantee of NATO's treaty, Macron answered, "I don't know," although he said the United States would remain an ally.
U.S. Secretary of State Mike Pompeo, in Leipzig ahead of the 30th anniversary on Saturday of the fall of the Berlin Wall that is seen by many as NATO's crowning achievement through its four-decade-long role blunting Soviet expansionism, said the alliance was perhaps one of the most important "in all recorded history."
Macron has said there is a lack of strategic coordination between European allies on the one hand and the United States and Turkey, with NATO's second largest military, on the other.
While France has traditionally had an ambivalent role in NATO, taking no part in its strategic military planning from 1966-2009 despite being a founding member, Macron's comments - a month before NATO's Dec. 4 summit in London - were unexpected.
NATO Secretary-General Jens Stoltenberg and many allies want to project an image of unity at the summit at a time of rising Chinese military might and what NATO leaders see as Russian attempts to undermine Western democracies through cyber-attacks, disinformation campaigns and covert operations.
NATO was shaken by Trump's portrayal of it as being in crisis at the last summit in Brussels in July, and its image of unity took a hit when Turkey defied its allies to launch a military incursion into Syria on Oct. 9.
Macron had earlier decried NATO's inability to react to what he called Turkey's "crazy" offensive and said it was time Europe stopped acting like a junior ally when it came to the Middle East.
In his interview, he also said the United States was showing signs of "turning its back on us", as demonstrated by Trump's sudden decision last month to pull troops out of northeastern Syria without consulting the allies, the French leader said.
German Chancellor Angela Merkel said he was overreacting.
"The French president has found rather drastic words to express his views. This is not how I see the state of cooperation at NATO," she told a news conference alongside Stoltenberg in Berlin.
Stoltenberg told Reuters that NATO had overcome differences in the past, citing the 1956 Suez Crisis and the 2003 Iraq War.
Once seen by some as a Cold War relic until Russia's 2014 annexation of Crimea, NATO needs all its 29 allies on side as it confronts militant attacks in Europe and seeks to defend against the threat of ballistic missiles from Iran to North Korea.
Macron lauded nascent European defense integration initiatives independent of the United States.
His so-called European Intervention Initiative has so far brought together nine willing militaries ready to react to crises near Europe's borders without NATO or the United States.
The European Union has also recently launched its own multi-billion-euro defense plans to develop and deploy military assets together after years of spending cuts that have left European militaries without vital capabilities and reliant on Washington.
"The European Union cannot defend Europe," Stoltenberg said in a speech in Berlin.
Since taking office in 2017, Trump has accused European NATO allies of not shouldering their fair share of the cost of defending Europe. He demanded they double NATO's defense spending goal of 2% of economic output, set in 2014.
They retorted that security is not just about spending targets, but all have since raised their defense outlays, though some remain short of the 2% objective.
In a change of policy, German Defense Minister Annegret Kramp-Karrenbauer said on Thursday Berlin would spend 2% of its economic output on defense by 2031, belatedly reaching the goal set by NATO leaders five years ago.
But with its military bases in Europe and nuclear warheads stored in five NATO countries, the United States remains the ultimate protector of European democracies against an increasingly assertive post-Soviet Russia.
In one sign of ongoing cooperation, the U.S. Air Force flew B-52 bombers from the U.S. mainland to train with British and Norwegian allies for almost a month in October at a time when China and Russia continue to modernize their militaries.