But French president Emmanuel Macron denied there had been an agreement to boost spending over 2%.
It was a classic performance for the one-time reality television star, whose "America first" mantra has translated into a sometimes-bullying style on the world stage, particularly with countries traditionally considered to be USA friends.
And Trump said that's all his doing.
It follows accusations in the United States, since Trump's 2016 presidential election win, that he owes his victory to the Russian president and that there may have been collusion between the Trump campaign and the Kremlin.
Also Thursday, Nato Secretary-General Jens Stoltenberg insisted that Georgia will one day join the world's biggest security alliance, despite separatist ambitions in parts of the former Soviet republic.
Over the two days of talks, Trump assailed leaders of the 70-year-old partnership, saying they weren't paying their fair share for defense and complaining that the United States wasn't getting any benefits from the billions of dollars it spends protecting Europe.More news: Puerto Rican T-shirt video controversy results in officer's resignation
In response, Lindsay Koshgarian, program director for the National Priorities Project which tracks Pentagon spending and its social implications, said that European leaders-and the people they represent-should be very wary about Trump's demand to increase military expenditures. He could not change France's budget for next year, which he had just presented to parliament.
By the end of that meeting, despite the pushback, Trump felt victorious.
The Allied Burden Sharing Report Act of 2018 would require the Defense Department "to resume compiling and submitting an extensive report that includes the common defense contributions of North Atlantic Treaty Organisation countries and other allies", including Gulf Cooperation Council countries, Australia, Japan, South Korea and New Zealand, according to a statement from Lee's office.
Romania will spend 2 per cent of its gross domestic product on defence, and Iohannis said other members "will try to spend more than 2 per cent". Trump called it "a fantastic meeting", speaking at a news conference before flying to Britain.
He also reportedly said that if the accelerated target - which was originally agreed for 2024 - is not honored the United States would "do our own thing", sources told the New York Times and Washington Post. Everyone's agreed to substantially up their commitment.
"Some are at 2 per cent, others have agreed definitely to go to 2 per cent, and some are going back to get the approval, and which they will get to go to 2 per cent", he said.
They say they will do more to encourage their businesses to remain engaged with Iran, though a number of firms have already said they plan to pull out as they also face sanctions following Trump's decision.