Merz said he had raised the issue directly with Trump in talks on Thursday, during the chancellor's first trip to Washington since taking office last month.

"The question that was asked was: do you have any plans to leave NATO? I can say it was answered with a very clear no," Merz said at an event hosted by the German family-owned business association.

"I have no doubt at all that the American government will stick to NATO now after we all said we're doing more, we're making sure that we can defend ourselves in Europe.

"I think this expectation was not unjustified. We have unfortunately been free-riders on American security guarantees for years and that's changing," he said.

Merz earlier this year spearheaded moves to exempt most defence spending from Germany's strict constitutional debt limits and has signalled his intention to raise military spending by tens of billions of euros.

During an Oval Office press conference Thursday, Trump welcomed Merz's moves to increase spending to patch up Germany's dilapidated military.

"I know that you are spending more money on defence now, quite a bit more money, and that's a positive thing," Trump said.

The US president has lobbied NATO partners to up their spending commitments to five percent of GDP from the current level of two percent.

Defence ministers from the US-led military alliance met in Brussels on Thursday to discuss a change to the spending target ahead of a NATO summit later this month.

US defence chief Pete Hegseth indicated allies were close to a deal to boost military budgets.

NATO chief Mark Rutte has put forward a proposal to meet Trump's target that would see members spend 3.5 percent of GDP in core military areas by 2032, and 1.5 percent on broader security-related items such as infrastructure.