Donald Trump and Emmanuel Macron's meeting in Paris had a frosty air after the French president said the EU needed its own army.
The US president tweeted on Friday to say the suggestion was "very insulting" and the continent should "pay its fair share to NATO".
He had arrived in the French capital earlier that day for a weekend of events commemorating 100 years since the end of the First World War.
Tensions were strained as Mr Trump and Mr Macron sat down in front of cameras at the Elysee Palace Saturday morning.
The US president reiterated his complaint about Europe's NATO contribution, and said: "Different countries have to also help and it's only fair… and the president (Mr Macron) and I very much agree on that."
While Mr Trump looked straight ahead, seemingly angry, Mr Macron responded: "I do agree… But it's unfair to have the European security today being assured just by the United States… I do believe that we need more European capacities – more European defence – in order to take this part of the burden."
A smiling Mr Macron finished by patting the US president on the knee.
President Macron of France has just suggested that Europe build its own military in order to protect itself from the U.S., China and Russia. Very insulting, but perhaps Europe should first pay its fair share of NATO, which the U.S. subsidizes greatly!
— Donald J. Trump (@realDonaldTrump) November 9, 2018
The row has soured relations between the two world leaders, who were said to have enjoyed a "bromance" when Mr Macron visited Washington DC in April.
Mr Trump toasted what he called a "great relationship" after hosting the French president at the first state dinner of his administration.
The two leaders are holding wide-ranging talks in Paris expected to delve deeper into European security, Syria and Iran.
It comes as Mr Trump cancelled his visit to a US war cemetery due "to bad weather" as world leaders mark Armistice Day.
Mr Macron's suggestion of a European army was pitched during an interview with radio station Europe 1 before a meeting of defence ministers from nine European countries to discuss how such a force would operate.
He told the station that Europe needed to be less reliant on the US, especially in light of Mr Trump's decision to pull out of a Cold War-era nuclear treaty with Russia.
"We have to protect ourselves with respect to China, Russia and even the US," Mr Macron said.
"When I see President Trump announcing that he's quitting a major disarmament treaty which was formed after the 1980s Euromissile crisis that hit Europe, who is the main victim? Europe and its security.
"We will not protect the Europeans unless we decide to have a true European army.
"We need a Europe which defends itself better alone, without just depending on the US."
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Mr Trump has repeatedly criticised the amount of money European nations commit to NATO compared to the US.
Earlier this year, during a private meeting with NATO leaders in Brussels, he suggested allies double their targeted 2024 spending commitment from 2% of their GDP to 4%.