Trump cut a jubilant figure after NATO's 32 countries agreed to his headline target of five percent of GDP on defence spending following two days of talks in The Hague.

Taking credit for a "fantastic" outcome that "no one really thought possible", Trump described the spending hike as "a monumental win for the United States".

"They said you did it, sir," he told a news conference. "Well I don't know if I did it -- but I think I did."

In a reassuring move for European allies worried over the threat from Russia, Trump signed off on a final leaders' declaration confirming "our ironclad commitment" to NATO's collective defence pledge that an attack on one is an attack on all.

NATO allies backed the spending increase to help counter a growing threat from Russia but also -- crucially -- to keep Trump engaged, with the US leader repeatedly suggesting Washington could withhold protection from lower-paying allies in Europe.

The deal appeared -- for now at least -- to have laid those gripes to rest.

The compromise hatched by NATO sees countries promise to dedicate 3.5 percent of GDP to core military spending by 2035, and a further 1.5 to broader security-related areas such as infrastructure.

While signing off on the target on paper, Spain has said it thinks it can fulfil NATO's demands while spending less -- earning a fresh rebuke Wednesday from Trump, who threatened to hit its trade interests in response.

But the pledge endorsed in The Hague allows Trump to claim triumph, while in practice providing some wiggle room for cash-strapped governments in Europe.

Diplomats said that behind closed doors Trump had given strong assurances of Washington's commitment as an ally and urged others to spend some of the new money on US weaponry.

- 'Couldn't have been nicer' -

Everything was choreographed at the gathering in The Hague to keep the volatile US president on board: from chopping back the official part of the meeting to putting him up overnight in the royal palace.

Underpinning the leaders' discussions on defence was Moscow's invasion of Ukraine, and in another sop to the demands of allies the United States allowed NATO to refer to the "long-term threat posed by Russia to Euro-Atlantic security" in the communique.

Though its language was watered down from previous years, the declaration also said allies would continue to support Ukraine "whose security contributes to ours" and could use money from the new spending pledge to fund military aid for Kyiv.

Ukraine's Volodymyr Zelensky played a less central role here than at previous summits -- with leaders wary of any bust-up after his infamous Oval Office shouting match with Trump.

But the US president did meet the war-torn country's leader on the summit sidelines, declaring afterwards the encounter "couldn't have been nicer" and Zelensky hailed a "substantive" meeting.

Trump also said he was talking to Russian President Vladimir Putin about the war, saying: "I think progress is being made."

That said, despite the insistence by NATO chief Mark Rutte that Ukraine's bid for membership remains "irreversible", the summit statement avoided any mention of Kyiv's push to join after Trump ruled it out.

- 'Not a rip-off' -

Trump had rattled allies on the summit's eve by appearing to cast some doubt on the validity of NATO's mutual defence clause -- known as Article Five of the alliance treaty.

But the pledge was reaffirmed unequivocally in the summit's final statement -- and Trump drove the point home at his closing press conference.

"I came here because it was something I'm supposed to be doing," Trump said in closing remarks to the press, when pressed on the mutual defence clause known as Article Five.

"But I left here a little bit differently," said the US leader -- who was visibly delighted at the red carpet welcome and the praise lavished on him by NATO's Rutte among others.

"Without the United States, they couldn't really have NATO. Wouldn't work," Trump said. "It will in the future, because now they're paying much more money."

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