Trump has long criticized NATO partners for not paying their fair share and had not previously confirmed he would attend the meeting, his first with the transatlantic alliance since his return to power.

"I can confirm he will be going to the NATO summit, yes," White House Press Secretary Karoline Leavitt said in a briefing when asked by AFP if Trump would attend.

Ukraine's war with Russia will also be on the agenda, with President Volodymyr Zelensky confirming on Tuesday that his country has been invited. Zelensky and Trump had a major Oval Office row in February.

Republican Trump threatened to withdraw altogether from NATO during his first term, and has since threatened to defend only those allies that he thinks are spending enough on defense.

His administration has also raised the prospect that it could look to shift forces away from Europe to focus on threats elsewhere like China -- while causing tensions with allies Canada and Denmark by threatening their territory.

His core demand is for NATO members to spend five percent of GDP on defense, claiming that Washington is bearing most of the burden for their defense.

None of NATO's 32 members -- including the United States -- currently hit that level.

To make him happy, alliance chief and former Dutch premier Mark Rutte has floated a proposal for 3.5 percent of GDP on direct defense spending by 2032, and 1.5 percent of broader security-related expenditures.

Such a deal could let Trump claim a win by reaching his headline figure even if not all of it is new spending.

Rutte's compromise deal received backing from heavyweights Germany and France in May, boosting its chances of going through.