Trump did not directly answer questions about whether he had threatened to take the USA out of the alliance, saying he "told people I'd be very unhappy if they didn't up their commitments very substantially".
Trump said he made his anger clear to allies on Wednesday.
Mr Trump said it's stronger than it was two days ago.
Sources close to the talks told DW's Teri Schultz that Trump demanded European NATO members meet the alliance target immediately, rather than increase spending gradually as agreed to at a previous NATO summit in 2014.
French President Emmanuel Macron, however, immediately denied that any agreement had been reached to increase expenditures beyond previously agreed targets.
"There is a communiqué that was published yesterday".
"(The) 2 per cent (figure) was a range, a goal, now it's a commitment, it was like this amorphous number out there and now it's a real commitment", he said.
Serena Williams comes back to reach Wimbledon semifinals
After the review confirmed the ball landed on the line, umpire Juan Zhang of China awarded the point to Cibulkova. The second set, was prolonged but the former Champion came through 7/5 after 1 hour and 29 minutes.
At the same breakfast (and on several other occasions later in the day), Trump blasted German Chancellor Angela Merkel for an energy deal her country has with Russian Federation, saying they are "totally controlled by Russian Federation", and a "captive" of the country.
Trump had spent his time in Brussels berating members of the military alliance for failing to spend enough of their money on defence, accusing Europe of freeloading off the USA and raising doubts about whether he would come to members' defence if they were attacked. But I said, ultimately we should be - in years in advance, we should be at 4 percent.
"Some are at 2%, others have agreed definitely to go to 2%, and some are going back to get the approval, and which they will get, to go to 2%", he said.
Painting a rosy portrait before he left Brussels, Trump added: "I can you tell you that North Atlantic Treaty Organisation now is a really a fine-tuned machine".
When Canadian Prime Minister Justin Trudeau said Canada would not be pushed around by the United States on trade, Trump responded with a tweet from Air Force One calling Trudeau "very dishonest and weak".
Stoltenberg said he had called the extra session because the allies felt the issue of burden sharing needed more discussion. Tens of thousands of people are likely to protest in the British capital on Friday, while Trump is outside the city at May's country residence Chequers, before visiting Windsor to meet the Queen.
Another big beef Trump seems to have with his allies are are their ties to Russian Federation (yes, seriously).
Rod Rosenstein expected to announce new indictment in Mueller probe
They used a network of computers around the world, a system paid for with cryptocurrency, to hide their identities. The group also actively targeted and hacked individual members part of the Clinton Campaign, the DOJ said.
There had been concern that President Trump might leave the alliance.
Trump stressed that NATO's budget had been unfair to the United States but now he was sure it would be fair.
"What they're doing is spending - at a much faster clip they're going up to the 2 percent level", Trump said. Add Donald Trump as an interest to stay up to date on the latest Donald Trump news, video, and analysis from ABC News.
"One thing you need in this alliance is predictability", an unnamed diplomatic official told NBC.
Speaking at a news conference before leaving Brussels, Trump said he would "of course" raise the issue of Russian interference in the 2016 USA election but continued to strike a friendly tone toward Putin, saying he considered him more a "competitor" than an enemy.
NATO Secretary General Jens Stoltenberg on Thursday told CNN that the organisation's member countries have committed to defence spending at two percent of GDP, but would not confirm US President Donald Trump's claim that the target was actually four percent.
"Throughout my life, my two greatest assets have been mental stability and being, like, really smart", the president tweeted.
RAF Ensign flown to mark RAF centenary
Following the service at Westminster, a royal flypast took place over Buckingham Palace. The royal family has a long history with the Royal Air Force.