Spanish Prime Minister Pedro Sanchez and Belgium Prime Minister Charles Michel were also singled out by Trump for undershooting on their spending targets when U.S. taxpayers, funding a defence budget worth about 3.6 percent of their national income, foot much of NATO's bills.
Trump said he had been "extremely unhappy" with allies' low levels of defense spending before the summit, but was pleased "they have substantially upped their commitment" during a "fantastic" unscheduled crisis meeting on Thursday morning.
Prime Minister Justin Trudeau is billing a pre-existing plan to grow military spending by 70 per cent over the next 10 years as Canada's answer to Donald Trump's persistent demand that North Atlantic Treaty Organisation allies spend two per cent of their GDP on defence.
Al Jazeera's diplomatic editor, James Bays, reporting from the Belgian capital, however, said that based on interviews with sources, "nothing it seems, in the closed-door meeting, was resolved".
During a post-summit briefing, Denmark's foreign minister, Anders Samuelsen, was one of several leaders who pointed to the president's unpredictability on whether the US would remain an ally of the North Atlantic Treaty Organization. "Tremendous progress has been made. It's been fantastic to see the level of spirit in that room".
Under fire for his warm embrace of Russia's Vladimir Putin, Trump on Wednesday also turned a harsh spotlight on Germany's own ties to Russian Federation, alleging that a natural gas pipeline venture with Moscow has left Angela Merkel's government "totally controlled" and "captive" to Russian Federation.
Poland has gone a step further, asking the U.S.to permanently station troops in the country. Trump also prepared to make a previously unscheduled public statement, the White House said.
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.
Will Smith Just Won the ''In My Feelings'' Challenge & Drake Agrees
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Trump had spent his time in Brussels berating members of the military alliance for failing to spend enough of their money on defense, accusing Europe of freeloading off the US and raising doubts about whether he would come to members' defense if they were attacked.
Trump heads to Britain on Thursday, where the government is in crisis over Brexit and where tensions with Russian Federation have spiked after London blamed Moscow for the death this month of a British woman from contact with the Novichok nerve agent.
Another NATO diplomat said Trump trampled on protocol by pointing at some leaders he said were not spending enough and addressing Merkel by her first name, referring to her as "you, Angela".
Despite reports of tensions between Trump and some of the US's closest allies, the president insisted that relations between the leaders remain "very strong".
When asked about that, Trump said he believed he could do that without Congressional approval but it was "not necessary".
The president also blamed the special counsel's probe into Russian meddling for harming U.S.
Brussels may dismiss this as typical Trumpian bluster, but my sense is that Trump is not bluffing. 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.
Two of her top government officials resigned earlier this week over negotiations on how to manage Brexit, including foreign secretary Boris Johnson, whom Trump has called a "friend".