Emmanuel Macron has warned that a lack of US leadership is causing the "brain death" of the Nato military alliance.
The French president said that the European Union must step up and start acting as a strategic world power.
"What we are currently experiencing is the brain death of Nato," Mr Macron told The Economist magazine.
He said the United States under President Donald Trump appears to be "turning its back on us", notably by pulling troops out of north-east Syria without notice.
Mr Trump surprised his Nato partners with last month's troop withdrawal. Nato plays no role in Syria, apart from helping the coalition fighting the Islamic State extremist group but the move was seen by Turkey, another Nato ally, as a green light to invade the region.
Mr Trump also wrong-footed the allies by announcing a troop draw-down in Afghanistan and then declaring that peace talks with the Taliban were cancelled after a bomb attack killed a US soldier.
Nato has played a major security role in the country since 2003, but its future there is now unclear.
Beyond that, the US leader publicly berated other leaders at a May 2017 summit for failing to boost their military budgets. Mr Trump's preoccupation with defence spending has been a constant theme since he came to office in 2016 and is expected to feature at the next Nato summit, in London on December 3-4.
Mr Macron said that the European members of the 29-nation alliance "should reassess the reality of what Nato is in the light of the commitment of the United States".
More broadly, Mr Trump's trade tariffs against the EU have rankled European members of Nato. And his decision to pull the United States out of the Paris climate agreement particularly annoyed Mr Macron.
In the interview, Mr Macron said that Mr Trump "doesn't share our idea of the European project".
He added that Europe stands on "the edge of a precipice" and must start thinking like a geopolitical power, otherwise it will "no longer be in control of our destiny".
But after talks with Nato secretary-general Jens Stoltenberg in Berlin, German Chancellor Angela Merkel rejected Mr Macron's claim.
She said: "The French president chose drastic words. That is not my view of cooperation in Nato and I think that such a sweeping blow is not necessary, even if we do have problems, even if we must pull together."
Mr Stoltenberg said: "We have to remember that any attempt to distance Europe from North America risks not only weaken the alliance, the trans-Atlantic bond, but also to divide Europe, so therefore we have to stand together.
"I welcome European unity, I welcome efforts to strengthen European defence, but European unity cannot replace trans-Atlantic unity," he added.
US Secretary of State Mike Pompeo and his German counterpart also stressed the importance of the Nato alliance.
Speaking after visiting the German village of Moedlareuth with Foreign Minister Heiko Maas, which was divided into two during the Cold War, Mr Pompeo told reporters it was the "remarkable work" of democratic nations that "created freedom and brought millions of people out of very, very difficult situations".
"I think Nato remains an important, critical, perhaps historically one of the most critical, strategic partnerships in all of recorded history," Mr Pompeo said.
Mr Maas also weighed in, saying he did "not believe Nato is brain dead", adding: "I firmly believe in international cooperation."