Johann Wadephul said NATO chief Mark Rutte had laid out a plan to reach "the five percent that President Trump demanded, which he considers necessary".

"And we follow him there," Wadephul told a meeting of the alliance in Turkey.

Berlin's signal of support will put more pressure on other European allies and Canada to strike a deal on spending at a NATO summit in The Hague next month.

Rutte has floated a proposal for allies to commit to 3.5 percent of direct military spending by 2032, and an additional 1.5 percent of broader security-related expenditure.

That overall plan has already got the backing of the United States.

It would hand Trump the headline figure he is demanding while giving enough wiggle room to European allies that are struggling just to reach NATO's current spending target of two percent of GDP.

Rutte declined to go into details of the discussions as foreign ministers gathered near the Turkish coastal resort of Antalya.

But he said broader spending, such as on infrastructure like bridges needed to move military hardware around, had to "be taken into account".

Italy's Foreign Minister Antonio Tajani announced that Italy had this week hit NATO's two percent spending target.

"This is the first step. Then it's possible to do more, it's possible to increase the money for defence," he said.

"I prefer to talk about security, because security is not only weapons."

Trump has rattled European allies worried about the menace from Russia by threatening not to protect countries that, in his eyes, do not spend enough.

None of NATO's 32 countries, including the United States, currently spend five percent of their GDP on defence.

Eastern members most worried about Moscow such as the Baltic states and Poland have already said they are willing to go beyond that level on direct military expenditures.