Nato leaders have arrived in The Hague for a summit hailed by German Chancellor Friedrich Merz as historic and aimed at securing peace in Europe for future generations.

It is US President Donald Trump’s first Nato summit since 2019 and all 32 leaders are set to commit to spending 5% of national output on defence and related infrastructure.

Ahead of his arrival, Nato Secretary General Mark Rutte sent him a pre-summit message, lavishing praise on his handling of Western alliance and the conflict in Iran.

“You are flying into another big success in The Hague this evening. It was not easy but we’ve got them all signed on to five percent,” Rutte wrote, in a message posted by Trump on social media.

He also congratulated Trump on his “decisive action in Iran, that was truly extraordinary and something no one else dared to do. It makes us safer.”

Asked later if it was embarrassing that his private message had been shared, Rutte told the BBC there was “absolutely no problem – there was nothing in it that had to stay secret”.

Western leaders have all had to navigate their relationships with Trump, known for his sometimes unpredictable handling of diplomacy. The two-day Nato summit has already been scaled back, apparently to accommodate his schedule.

Nato leaders gathered for a group photograph before joining King Willem-Alexander and Queen Maxima of the Netherlands for dinner.

The Nato secretary general earlier told his European colleagues to stop worrying about the US commitment to the Western alliance and focus on investing in defence and supporting Ukraine.

He insisted the US president and senior leadership had a “total commitment” to Nato, that came with an expectation of matching American military spending.

Rutte said Europe and Canada had already committed to more than $35bn (£26bn) in military support for Ukraine this year.

Twenty people were killed in Russian attacks on Ukraine on Tuesday, and the German chancellor said every attempt to bring Russia to the negotiating table had so far been unsuccessful.

Missile attacks on the eastern city of Dnipro and the nearby town of Samar killed 17 people and wounded another 160, according to Ukrainian officials. Eighteen children were wounded in the attack on Dnipro, which damaged a kindergarten, schools and a passenger train, they said.

An earlier missile strike on Sumy in the north-east killed three people, including a child.

Zelensky, who has arrived in The Hague, is due to meet Donald Trump on the sidelines of the Nato summit. The Ukrainian leader had a notoriously difficult meeting with the US president at the White House in February, before a more constructive exchange at Pope Francis’s funeral at the Vatican in April.

Nato member states are expected to approve a major new investment plan which will raise the benchmark for defence investment to 5% of GDP.

Many of the allies are far below the commitment to spend 3.5% of GDP on defence by 2035, but the German government backed a budget deal on Tuesday to hit that target by 2029.

Some €62.4bn (£53bn) will be spent on defence in 2025, rising to €152.8bn in 2029, partly financed by debt and special funds.

“We’re not doing that as a favour to the US and its president,” the German chancellor told parliament in Berlin on Tuesday. “We’re doing this out of our own view and conviction, because Russia is actively and aggressively endangering the security and freedom of the entire-Euro-Atlantic area.”

During the summit, Merz is due to meet UK Prime Minister Sir Keir Starmer and France’s President Emmanuel Macron.

Mark Rutte has spent much of the nine months since becoming Nato Secretary General working to get allies to commit to the 5% target. The figure is more than double Nato members’ current 2% guideline and seemed unthinkable – and unrealistic – to most when President Trump first set it in January.

The two-day Nato summit was to begin with a dinner hosted by the Dutch king, with a working session of under three hours on Wednesday and an expected five-paragraph statement at the end.

The wording of the commitment in the statement is key.

While 3.5% of of the target spending will cover core defence requirements, 1.5% will be spent on “defence-related expenditure” – a suitably broad expression that encompasses investments in anything from cybersecurity to infrastructure.

Reaching the 3.5% core defence spending target will still require a significant adjustment for the majority of Nato countries. Out of 32 allies, 27 spend under 3%, with eight hovering well below the 2% threshold set by the alliance in 2014.

On Monday, Prime Minister Keir Starmer pledged that the UK would meet the 5% target by 2035.

He said the UK had to “navigate this era of radical uncertainty with agility, speed and a clear-eyed sense of the national interest”. The UK government said it expected to spend 2.6% of GDP on core defence within two years, alongside 1.5% on defence-related areas.

At the bottom of the rung is Spain, whose defence spending is below 1.3%.

Madrid would need to more than double its funding to meet Rutte’s new target – something that Socialist Prime Minister Pedro Sánchez has long resisted, arguing it “would not only be unreasonable but also counterproductive”.

It would also, crucially, be unpopular at home – not least among his left-wing governing coalition – at a time when Sánchez’s government is teetering.

On Sunday Sánchez said Spain had reached a deal that would see it exempted from the target – something Rutte swiftly pushed back on. “Nato is absolutely convinced Spain will have to spend 3.5% to get there,” he said on Monday.

Sánchez’s suggestion of a lower spending threshold was enough for Belgium and Slovakia to also express interest in an exemption – denting Rutte’s hard-won image of a united alliance.

“I can assure you that for weeks our diplomats have been working hard to obtain the flexibility mechanisms,” said Belgium’s foreign minister Maxime Prévot. Brussels’ spending is currently at 1.3% – and Slovakia has also said it reserves the right to decide when to meet the new target.

Despite their comments, all 32 states are expected to sign up to the new pledge.

As Nato leaders and the leaders of more than a dozen partner states made their way to The Hague, train travel from Schiphol Airport near Amsterdam was badly disrupted after cables were damaged by fire.

Security Minister David Van Weel said sabotage could not be ruled out. “It could be an activist group, it could be another country. It could be anything,” he told public broadcaster NOS. “The most important thing now is to repair the cables and get the traffic moving again.”