Not only did Trump demand on Twitter on Thursday that countries meet the 2% level by this year, not 2024, but he also said all countries should eventually hit 4%, which is more than even the U.S. now spends.
But French president Emmanuel Macron denied there had been an agreement to boost spending over 2%.
Trump claimed member nations had agreed to significantly boost their defence budgets and reaffirmed - after days of griping that the USA was being taken advantage of by its allies - that the US remains faithful to the accord.
President Macron said: "There is a communique that was published yesterday".
Heading into the North Atlantic Treaty Organisation meeting, Trump said, "I'd be unhappy if everyone didn't up their commitments substantially".
Others say Congressional approval would be required - and would be unlikely to be forthcoming.
Earlier Thursday, Trump called out USA allies on Twitter, saying, "Presidents have been trying unsuccessfully for years to get Germany and other rich NATO Nations to pay more toward their protection from Russian Federation".
Several diplomats and officials said, however, that his undiplomatic intervention - including pointing at other leaders and addressing Merkel as "you, Angela" - had irritated many.
But now, according to media reports, Trump has threatened to withdraw the US from the North Atlantic Treaty Organization (NATO, ) or to change its pivotal role in the alliance, over the matter. He laid into Germany for not spending more on its military while becoming increasingly dependent on Russian Federation for its energy needs. "I would imagine that President Trump will be well prepared by the National Security Council and all of his people, knowing that dealing with Putin, who will be ultra-prepared, tough, ruthless. not want to give nothing".
Trump said there had been "tremendous progress" after his "firm" warnings during the tense two-day meeting in Brussels, during which he singled out Germany for special criticism.
He said the US "pays tens of Billions of Dollars too much to subsidize Europe" and demanded that members meet their pledge to spend 2 percent of GDP on defence, which "must ultimately go to 4%!"
But he said that since a year ago around an additional 33 billion dollars, not including the United States, had been raised and it was now "unnecessary" to withdraw from the organisation. They all made commitments and they will be up to 2%.
Shelby pointed to the importance of Trump being properly briefed ahead of the sit-downs. Describing the dynamics of the talks, he said, "I was using the term a lot today: burden-sharing". "I made clear that we are on this path". US Turkish relations have recently been strained because of issues ranging from Syria to Iran, but some diplomats say the two leaders - both criticised for their polarising politics - have established a bond.
Asked what would be the best possible result from his meeting with Putin, Trump said: "What would be the ultimate?" He said the allies had confirmed their intention to meet the goal of 2 per cent by 2024 and no more.
"The commitment was at two percent and that'll be going up quite a bit higher than that", he said.