Just eight countries are forecast to reach the two per cent goal this year, and 15 by 2024.
"It will be over a relatively short period of years", Trump said.
The summit's dramatic, chaotic conclusion - complete with the US president suddenly making demands following a formal communique - bore a striking similarity to Trump's departure from last month's G7 meetings in Quebec.
"That is all", Macron said.
Before the summit began, NATO Secretary General Jens Stoltenberg said seven nations-plus the USA -are already delivering on the commitment, up from three in 2014. And he said Canada has promised to reverse a decline in military resources with an eye towards the two per cent target. "Much stronger than it was two days ago", Trump said in an unscheduled statement.
The U.S. president said if other countries don't meet NATO's 2 percent of GDP spending target for defense, the U.S. would go it alone, DPA reported, citing unnamed sources.
Trump himself accused Germany of being a "captive" of Russian Federation due to a multi-billion-dollar pipeline deal, complaining that Germany and other North Atlantic Treaty Organisation allies "pay only a fraction" of the cost of defending Europe. Of the alliance, he said it was "very unified, very strong, no problem".
He triggered an emergency session on the spending issue, before emerging from the turmoil to say "I believe in Nato" in response to reports that he had threatened to pull out. "But I'll very firmly ask the question".
"Russia has shown itself to be an adversary of the United States and our allies and a serious threat to global peace, security, and stability", they wrote to Trump. Citing the alliance's Secretary-General Jens Stoltenberg, he said: "Secretary Stoltenberg gives us total credit, meaning me, I guess, in this case, total credit".More news: Donald Trump makes his first trip to Britain
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"For Nato to be sustainable and successful, all countries need to step up to the plate". "Because I said it was unfair". "There is a great, great spirit leaving that room".
Stavridis said he thinks it's probably in Canada's interest to invest in better interoperability capabilities with other allied forces - but at the end of the day the decision to increase defence spending is ultimately up to Canadians, not Americans.
But Warsaw has at times been nervous about Trump's fondness for Russian President Vladimir Putin, with whom Trump will meet Monday in Helsinki, Finland. President Trump himself should be the one to bring this message to Putin.
Trump's campaign and transition team have been accused of colluding with Russian agents in an effort to influence the 2016 USA election against Hillary Clinton.
Mr Trump had opened the first day of talks in Brussels yesterday with a public diatribe against Germany, the second biggest state in the Western defence alliance, before the mood appeared to have calmed as the summit went into its second day, focusing on operations beyond Europe. I mean, it's one of those things. John McCain (R-Az) - have called for the summit to be called off, especially if Trump is not willing to take Putin to task for the Russian meddling.
Trump brushed off the protests, saying, "I think they like me a lot in the UK".
"The numbers have gone up like a rocket ship. and they're going to be going up further", he said.
"What they're doing is spending - at a much faster clip they're going up to the 2 percent level", Trump said.