The White House confirmed he had made the remarks during the Western military alliance’s summit in Brussels.
The meeting also saw Mr Trump single out Germany for criticism over its defence spending.
Nato’s secretary-general said the main focus should be on all members reaching the current target of 2% of GDP.
Jens Stoltenberg declined to answer a specific question about Mr Trump’s remarks, but told reporters: “I think we should first get to 2%, focus on that now… the good thing is that we are moving to that.”
For decades after the end of the Cold War, he said, Nato countries had cut defence budgets as tensions fell – and now needed to increase them at a time when tensions were rising.
Previous US presidents have urged Europe to take more responsibility for their defence and reduce the burden on US taxpayers of maintaining forces in Europe long after the end of the Cold War – but none as bluntly as Mr Trump.
Confirming the Mr Trump’s comments, White House spokeswoman Sarah Sanders said: “President Trump wants to see our allies share more of the burden and at a very minimum meet their already stated obligations.”
The Brussels meeting comes…