'Why are there only 5 out of 29 countries that have met their commitment?
He continued the attack Thursday, complaining that "Germany just started paying Russian Federation, the country they want protection from, Billions of Dollars for their Energy needs coming out of a new pipeline from Russian Federation".
In a series of tweets from Brussels, Trump said "Presidents have been trying unsuccessfully for years to get Germany and other rich NATO Nations to pay more toward their protection from Russian Federation".
Trump claims the USA is already spending the equivalent of four per cent of its GDP on defense, but experts say the actual figure is 3.57 per cent.
In remarks later during the summit, however, President Trump increased pressure on allies over burden sharing, calling on allies to double defense spending targets to 4 percent, the White House confirmed.
It followed an uncomfortable first round at the summit where anxious Western allies were subjected to the USA president's "America first" approach. "That is very good, especially for people in eastern Germany".
Trump and first lady Melania Trump arrived in Belgium Tuesday for the summit, ahead of meetings later this week with British Prime Minister Theresa May in Britain and Vladimir Putin in Finland. Trump said in a tweet hours after he raised the issue during the NATO Summit in Brussels.
Reporters there noted that Kelly looked fairly uncomfortable as Trump made the comments.
The US intelligence community has concluded that Russian Federation interfered in the 2016 election to boost Mr Trump's candidacy, and warns of further attempts at interference both in the 2018 midterms and in European elections.
Stoltenberg said it had been appropriate and understandable for defence spending to fall after the end of the Cold War, but the alliance had now recognised the need to bring it back up, with member countries adding billions to their defence budgets.
The president is expected to meet with the leaders of Azerbaijan, Romania, Ukraine and Georgia before he travels to London Thursday.
Invited leaders from non-NATO countries Afghanistan and Georgia were asked to leave along with most North Atlantic Treaty Organisation leaders' retinues of officials, as the heads of state and government of the Western alliance sought to deal with the man whose nation commands much of the budget and forces for Europe's defense. The United States pays about 67 percent of its gross domestic product on defense, more than any other nation, although only 3.5 percent is NATO-related.
The meeting also saw Mr Trump single out Germany for criticism over its defence spending. "Because of that we can say that we can make our independent policies and make independent decisions".
The defense minister agreed with Trump about defense spending.
Instead, a series of events - a black-tie dinner with business leaders, a meeting with May and an audience with Queen Elizabeth II - will happen outside the bustling city, where Mayor Sadiq Khan has been in a verbal battle with Mr. Trump.