Allies would be increasing spending by $33 billion or more, he added.
"We are paying for far too much of Nato", Trump said.
Trump said there had been "tremendous progress" and that allies were "going to up it at levels they've never seen before".
Striking a strident tone at the summit, Trump's aspirational target of 4% of gross domestic product was above the United States own spending on defence. The U.S.is paying for Europe's protection, then loses billions on Trade.
"What will be said if President Trump says, 'Look, President Putin".
He said Russian Federation basically controls Germany because of German energy dependence on Moscow. Most officials and the invited leaders of non-NATO Afghanistan and Georgia were ushered out. In the afternoon, he heads to his next stop: the United Kingdom.
The Post reports that the Munich-based news outlet Süddeutsche Zeitung, one of Germany's largest news organizations, ran a story about the president's slams against Germany with the headline: "It is not only bad, it is catastrophic". "It's really extraordinary that Donald Trump has to be the person to point out that the emperor in Europe has no clothes".
North Atlantic Treaty Organisation leaders held the emergency session to discuss US President Donald Trump's repeated demands that allies meet the a pledge to spend 2 percent of GDP on defense.
Others in the room, including the Lithuanian president whose country is among the most nervous of Russian ambitions, denied a suggestion that Trump had threatened to quit the alliance.
Earlier in the day, Trump was on the attack, going after America's allies even as he refused the day before to call Putin an adversary of the United States.
Later Mr Trump and German chancellor Angela Merkel had a face-to-face meeting, where the row continued.
"I have to tell you that the atmosphere last night at dinner was very open, was very constructive and it was very positive, " Kolinda Grabar-Kitarovic, the president of Croatia, told reporters.
The mood was already prickly ahead of the summit, prompting a terse exhortation from the European Union's President Donald Tusk for Trump to "appreciate" his allies and reminding him that Europe had come to its aid following the 9/11 attacks.
The conversation was "positive", one official said.
The meeting brought together Mr Trump and Canada's prime minister Justin Trudeau, who irritated the United States president at the G7 by declaring that his country would not be pushed around. In a tweet Tuesday, he said: "Will they reimburse the USA?"
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