In a media conference where the US President again called himself a "very stable genius" and referenced his electoral college victory in the 2016 election, Mr Trump said he considers Russian President Vladimir Putin as a "competitor" rather than an enemy.
(From L to R, first row) German Chancellor Angela Merkel, Belgian Prime Minister Charles Michel, NATO Secretary General Jens Stoltenberg, U.S. President Donald Trump and British Prime Minister Theresa May attend the opening ceremony at the 2018 NATO Summit at NATO headquarters on July 11, 2018 in Brussels, Belgium.
The president continues to turn decades of American diplomacy on its head, says former US ambassador to NATO Nicholas Burns on MSNBC's Morning Joe Wednesday.
When asked about the footage, Trump's press secretary Sarah Huckabee Sanders said Kelly was simply "displeased because he was expecting a full breakfast and there were only pastries and cheese", the Washington Post reported.
Germany, Europe's biggest economy, spends just 1.24 per cent, compared with 3.5 per cent for the US.
Trump's demand jolted the transatlantic alliance at the conclusion of this week's Brussels summit and, in the words of one diplomat briefed on the events, sent "everyone into a tailspin".
Sources familiar with the first round of closed-door talks on Thursday told the Reuters news agency that Mr. Trump carried his firm stance on military spending from Twitter into the meeting rooms.
Germany now spends 1.24% of its GDP on defense, and has committed to hitting 2% by 2024, something that Trump, and other United States leaders before him, have tried to hasten.
The meeting brought together Mr Trump and Canada's prime minister Justin Trudeau, who irritated the USA president at the G7 by declaring that his country would not be pushed around.
He complained the United States "pays tens of Billions of Dollars too much to subsidize Europe" and demanded that member nations meet their pledge to spend 2 percent of GDP on defense, which "must ultimately go to 4%!"
"The United States' commitment to North Atlantic Treaty Organisation remains very strong", Trump said during the surprise news conference.
Trump touched down in Brussels aboard Air Force One hot on the heels of a stern warning from the EU's top official that America should "appreciate" its allies.
Stoltenberg estimated European allies and Canada will add $266 billion to their military spending by 2024 and said, "this is really adding some extra momentum", apparently meaning Trump's pressure.