"Article Five, he has not undercut. He has committed to NATO, he has committed to Article Five," Rutte told AFP in an interview.

Trump has rattled allies by threatening to only defend those he thinks are spending enough on defence as he pushes them to ramp up their military budgets.

His administration has also raised the prospect that it could look to shift forces away from Europe to focus on threats elsewhere like China.

"The agenda is not for the US to leave NATO or to leave Europe, the US is here. They will pivot more towards Asia, so that might, over time, mean that they have to rebalance," Rutte said.

"But there is now and there will remain in Europe a nuclear and also a conventional presence of the United States."

European countries have said that if Trump does plan to withdraw forces from the continent, he needs to coordinate with them to not leave gaps in the face of Russia.

"I assume and I expect that will be done in the spirit of no surprises," Rutte said.

The NATO head defended his own refusal to criticise the volatile US leader, insisting he saw "eye to eye" with Trump on efforts to bolster spending and bring the war in Ukraine to an end.

"When it comes to the issues I'm focused on, and that is Ukraine, that is NATO territory, we are really on one page," he said.

Rutte was speaking after a meeting of ally foreign ministers where US Secretary of State Marco Rubio demanded they agree on a "realistic path" to spending five percent of GDP on defence.

That figure appears well out of reach for most allies and is even considerably above what the United States currently spends.

Rutte said he would now launch a "content-driven process" studying the military requirements needed as the alliance looks to come up with a new spending target for a summit in The Hague in June.

"I think you now need to get to a number, potentially, be it in hard billions or a percentage, but then also a pathway together," he said.

- China 'threat' -

Washington has sparked fears in Europe that it could be looking to draw closer to NATO's number one nemesis Russia as it has reached out to Moscow to end the war in Ukraine.

Rutte insisted that Moscow remained the main threat for all NATO -- and not just Europe.

"Yes, to the whole of the alliance, as we have agreed," he said.

He said in addition that he viewed China as a "threat", a possibly controversial view inside the alliance which still refuses to label Beijing a direct menace.

"If you ask me, personally, I would say there's also a threat. I know NATO language is a bit more careful," Rutte said.

"But China, with the immense investments they are making in the military, more navy ships than the US has, a thousand nuclear warheads... Yeah, it's really ramping up."