NATO leaders must have "real dialogue" about the future of the military alliance, according to French President Emmanuel Macron.
Ahead of a summit of NATO leaders in London next week, Mr Macron said "a real alliance is action, decisions, not words".
At a joint press conference with NATO Secretary General Jens Stoltenberg in Paris, Mr Macron posed a series of questions about the alliance.
It comes just weeks after he described NATO as "brain dead".
"NATO is an organisation of collective defence," Mr Macron said.
"Against what, against who is it defending itself? Who is our common enemy? What are our common topics? This question deserves clarifications."
Mr Macron said he was "glad" his recent criticisms of NATO have acted as a "wake-up call" and that it was "irresponsible" to just discuss financial and technical matters.
He voiced his regret that the two previous NATO summits were focusing "only on how to alleviate the financial cost for the United States".
US President Donald Trump has repeatedly called for other members of the alliance to increase their spending on defence, even threatening to pull the US out of NATO.
The US spends more on defence than all other 28 allies combined.
Mr Macron called on NATO to focus on issues including maintaining peace in Europe, relations with Russia, the role of Turkey in NATO and who the alliance's enemies might be.
He urged for a return to dialogue with Russia that is "lucid, robust and demanding" to enhance confidence and security on the continent.
He also said the alliance needs to focus on extremist groups as the common enemy.
However, Mr Stoltenberg played down concerns of divisions inside the alliance.
"In uncertain times we need strong multinational institutions like NATO," he said.
"The paradox is that while questions are being asked about the strength of the transatlantic bond, North America and Europe are doing more together than they have done for decades."
Mr Stoltenberg also said the US will pay less into the military alliance's budget from next year, with Germany stepping up contributions to fill the gap.
He said a new cost-sharing formula has been agreed and that "the US will pay less, Germany will pay more".