"I'm absolutely convinced this alliance is there to stay with the US. Their commitment is absolutely clear," Rutte said on the eve of a meeting of NATO foreign ministers.

In just over two months in office, Trump's administration has raised the prospect of withdrawing forces from Europe, reached out to number one enemy Russia over Ukraine, and threatened the territory of Canada and Denmark.

Trump is also expected to announce trade tariffs later Wednesday that would hit the economies of NATO countries.

"I know there has been some tough language. I know that there have been allies, for example, on this side of the pond being worried about the long-term commitment of the US to NATO," Rutte said.

"The Americans have stated again and again: 'We are committed to NATO. We are committed to article five'," Rutte said, referring to the alliance's collective defence pledge.

Ahead of a summit in The Hague in June, Trump is demanding that allies ramp up defence spending -- with Washington insisting on a new target of five percent of GDP.

"This commitment comes with a clear expectation, expectation that on this side of the Atlantic and Canada, we will spend more," Rutte said.

Nervous NATO allies are set to press US Secretary of State Marco Rubio to lay out Washington's thinking on the future of NATO and Ukraine during two days of talks in Brussels starting Thursday.

Diplomats say they hope Washington's top diplomat will give more details on Trump's push for a deal with Moscow, and also clarity if there are plans to withdraw US forces from Europe.