Donald Trump and Frenchman Emmanuel Macron have both said Europe should pay more of its defense costs the day after the US president rejected the idea of a European army.
Mr. Trump is in Paris before events marking the end of the First World War.
He said the US wanted "a strong Europe," but the defense law "has largely turned against the United States."
Mr. Macron said he agreed that "we need a much better burden-sharing within NATO" – the US-led alliance.
"If President Trump has to protect one of the states of the United States, he will not ask France or Germany or any other country for funding, so I think we need more investment," he said.
Some 70 world leaders meet in Paris for ceasefire events that ended World War I, signed Sunday 100 years ago.
- May pays tribute to the fallen in France and Belgium World War I.
- What do the US do for NATO?
The unit's Trump-Macron unit came despite previous tensions that arose when the French leader said the EU needed a common army to deal with threats from the US, China and Russia.
"We have to protect ourselves with regard to China, Russia and even the United States of America," he told French radio station Europe 1 on Tuesday.
"I want to build a real security dialogue with Russia, a country that I respect, a European country – but we must have a Europe that can defend itself without relying solely on the United States."
Trump furiously responded with a tweet on a Friday night and wrote: "French President Macron has just suggested that Europe should build its own military to protect itself from the US, China and Russia. NATO share heavily subsidized by the US! "
Mr Macron has already substantially increased defense spending to reach the NATO target of 2% of GDP for defense.
He also oversees the formation of a European Force, a nine-nation company much smaller than an actual army supported by Germany and the United Kingdom.
What is the plan for Armistice Day?
After a one-hour round of talks, Messrs. Trump and Macron were invited to lunch with their wives Melania and Brigitte.
On Saturday afternoon, Mr Macron will meet German Chancellor Angela Merkel at Compiegne in northern France, where the Allies and Germany have signed the truce.
In the evening, the heads of state meet for dinner in Paris.
Donald Trump had planned to visit two American cemeteries over the weekend, but later canceled his trip to the Ainse-Marne American Cemetery and Memorial due to "scheduling and logistical difficulties due to the weather."
Gen John Kelly, the chief of staff of the White House, will participate in his name.
Trump is also expected to attend a dismal memorial service at the Tomb of the Unknown Soldier, a monument to France that fell under the Arc de Triomphe in Paris.
Early Saturday morning, he tweeted, "Is there anything better to celebrate than the end of a war, especially one that was one of the bloodiest and worst of times?"
On Sunday afternoon, Mr. Macron and Mrs. Merkel attend a peace conference – the Paris Peace Forum – with leaders such as Putin and the Turkish Recep Tayyip Erdogan.
However, Mr. Trump will not be present, which his national security adviser John Bolton attributed to a "urgent" journal.
The truce 100 years later
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Living History: Why "indecent" ceasefire parties ended
Will Trump meet Putin?
The status of this proposed meeting has changed repeatedly in recent weeks.
On Wednesday, the Kremlin said the two would hold a "short lunch" at the Élysée Palace in Paris, but the US still opposed that day.
"I do not think we have anything planned in Paris and I'm coming back very quickly," the president said. "I do not think we have time for this meeting."
The two men are meeting for world leaders lunch on Sunday, but it remains to be seen if a more formal discussion will eventually materialize.