The US president fired off a barrage of damning tweets aimed at the EU, Canadian Prime Minister Justin Trudeau and NATO allies – including Germany.
He also questioned the future of Nato as he attacked European countries for failing to pay their share towards the continent’s defence.
The UK is one of the few members states that pays the target of spending two per cent of its gross domestic product on defence.
Trump tweeted: “The U.S. pays close to the entire cost of NATO – protecting many of these same countries that rip us off on trade (they pay only a fraction of the cost – and laugh!)
“The European Union had a $151 billion surplus – should pay much more for military!
“Germany pays 1 percent (slowly) of GDP toward NATO, while we pay 4 percent of a much larger GDP. Does anybody believe that makes sense?
“We protect Europe (which is good) at great financial loss, and then get unfairly clobbered on trade. Change is coming!”
His extraordinary outburst on Monday came after he left the G7 summit in Canada early to fly to Singapore for a landmark meeting with Kim Jong-Un.
The stormy G7 talks over the weekend saw Trump infuriate fellow leaders by arriving late, ignoring the dress code and leaving early.
He also delivered a personal snub to Theresa May by refusing to name her in his list of G7 friends.
The explosive comments are now sure to set the scene for further clashes at the Nato summit next month.
Speaking in the Commons, Theresa May admitted the summit was “difficult” and cautioned against a tit-for-tat retaliation after tariffs were imposed on American imports of European steel and aluminium.
She said: “This was a difficult summit, with at times some very candid discussions.
“But the conclusion I draw is that it is only through continued dialogue that we can find ways to work together to resolve the challenges we face.
“The countries round the G7 table have been pillars of the rules-based international order which has benefited all our citizens and, I believe, the world as a whole. “The United Kingdom, with our allies and partners, will continue to play our part in promoting that order to the benefit of all.”