The US President said "4% is the right number" on NATO defence spending. (Image: PA).
Donald Trump has backed down over threats to pull the US out of NATO after other leaders agreed to increase defence spending "like they never have before".
It had been reported NATO was holding an emergency session as a result of the US President's demands.
At a press conference, President Trump was asked whether he had threatened to leave the alliance over the spending of other nations. He replied:
"I told people I'd be very unhappy if they didn't up their commitments very substantially.
"Yesterday, I let them know I was extremely unhappy with what was happening and they have substantially upped their commitment."
The alliance was now "much stronger than it was two days ago", he said.
"I believe in NATO."
Following the summit, the US President tweeted:
Downing Street has backed the US President's calls for other nations to increase their defence spending. A spokeswoman said:
"We have always been clear that we think it's right that NATO countries pull their weight to ensure collective security.
"There is an agreement to move towards 2% [of GDP] by 2024 but we think there is more to be done.
"We are already paying above the 2% target."
In Brussels, Donald Trump went on to say: "I told people I would be very unhappy if they didn't up their commitments very substantially."
President Trump said "tremendous" progress had been made on extra spending and said he believed in NATO but the skewed levels of funding were "unfair" on the US.
"We made a tremendous amount of progress today," he told reporters.
"The United States' commitment to NATO remains very strong," he said.
Mr Trump said that NATO would soon discuss member defence spending at a higher level than the alliance's target of 2% of GDP.
"I think 4% is the right number," he said.
The US President insisted NATO leaders were now "putting up a lot" and it was "unnecessary" to pull the US out of the organisation.
He said Germany had agreed to increase "very substantially" the timescale for increasing funding.
"The people have stepped up today like they have never stepped up before," he said.
Mr Trump said everybody in the room had thanked him, including NATO Secretary General Jens Stoltenberg, and described himself as a "very stable genius".
He then claimed that the Secretary General gave him "total credit" for securing additional funding agreements for the alliance.
All NATO nations will be up to 2% on defence spending over a "relatively short period of years", he said.
Earlier, Mr Trump said alliance countries were not spending "nearly enough" on defence - despite billions of additional dollars being invested since he issued a warning over the US' future contribution to the alliance.
The president tweeted: