President Donald Trump is pressuring allies to agree to a new spending target of five percent of GDP when leaders meet in June in The Hague -- a level none of NATO's 32 members currently reaches.

Rutte has floated a compromise deal to commit to 3.5 percent of direct military spending by 2032, as well as another 1.5 percent of broader security-related expenditure.

US NATO Ambassador Matthew Whitaker threw Washington's weight behind the proposal to allow a wider scope of spending to make up the five percent.

"This new Hague investment pledge or plan is going to include all of the capability targets necessary for NATO allies to deter and defend, but it also includes things like mobility, infrastructure, necessary infrastructure, cyber security," he told journalists.

"It is definitely more than just missiles, tanks and howitzers, but at the same time, it's got to be defense related. It is not a grab bag for everything that you could possibly imagine," Whitaker added.

NATO foreign ministers are set to meet Wednesday in the Turkish resort of Antalya for two days of talks aimed at thrashing out details for the June summit in The Hague.

The flexible approach from Washington should help Rutte forge a deal as it grants more leeway to allies still scrambling to hit NATO's current spending threshold of two percent.

Europe has ramped up its defence spending since Russia launched its 2022 invasion of Ukraine.

But a number of countries including Canada, Italy and Spain are only due to hit two percent this year.

Diplomats say that allowing countries to count broader security-linked spending should help those grappling with constrained budgets agree to further hikes.