KEIR Starmer has refused to guarantee that he will meet his flagship commitment on defence spending within his first term in office, despite a “cast iron” promise to get there.

The Prime Minister, who will meet US President Joe Biden and other Nato leaders on Wednesday at a summit to mark the alliance’s 75th anniversary, is pressing for European nations to increase defence spending.

But decisions on reaching the UK’s goal of spending 2.5% of gross domestic product (GDP) will follow a wholesale defence review being launched next week and must comply with the Government’s strict “fiscal rules” on spending and borrowing.

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Starmer will hold talks with Biden in the White House on Wednesday afternoon as the US President faces domestic pressures over his age and suitability to run for a second term.

The prospect of Donald Trump being returned to the White House in November’s election is a cause for concern in the alliance given his past criticisms of Nato and his threats to reduce aid to Ukraine.

European Nato states face shouldering a greater burden as part of a drive to “Trump proof” the alliance should the Republican candidate return to office and weaken US commitment to the 32-nation bloc.

Speaking to reporters, Starmer was repeatedly pressed on whether the goal of spending 2.5% of GDP would be reached within his first term.

He said: “We are committed to the 2.5%, as I have said before the election and I say again after the election. That is obviously subject to our fiscal rules, but the commitment is there.

“The strategic review will take place, that will happen next week, and we will set out the details of that.

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“The manifesto commitment was that it would take place within a year, I would like it to be quicker than that if I’m honest and we’ll set out the details about how we are going to do it.”

Officials have described 2.5% as a “cast iron commitment” but the announcement a strategic defence review will be launched next week did not include any timetable for ramping up spending.

Before his election defeat, Rishi Sunak had committed to reach 2.5% by 2030 at a total cost of £75 billion over six years.

Nato members have an official goal of spending 2% of GDP on defence and 23 members are now thought to have reached that level.

But in the context of this year’s US election, Starmer acknowledged more was needed to be done, particularly on locking in support for Ukraine and its president Volodymyr Zelensky, who is at the summit.

“On the question of how we show that commitment here at this summit, given there is going to be an election in America later this year, I think it’s very important at this summit, and I think there is a real opportunity for real unity,” Starmer told reporters.

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“It’s the largest group of Nato countries, together with the additions that we’ve got, and the package that we are seeking to advance, it goes beyond the support that’s been put in before and will be locked in – I hope – at this Nato conference.”

There would be a financial package, military aid and an industrial strategy to support Ukraine, he indicated.

Starmer confirmed that decisions on the use of UK-supplied long-range Storm Shadow missiles were for the Ukrainian armed forces to make, indicating they would be permitted to strike against targets within Russia.

The UK military aid was “for defensive purposes but it is for Ukraine to decide how to deploy it for those defensive purposes”.

The Russian strike on a children’s hospital in Kyiv on Monday was a “tragic backdrop to this summit” and “strengthens the resolve” of Nato against Vladimir Putin, he said.

Asked if it was a war crime, the Prime Minister said: “In relation to its specific category within international law, that will be a matter for others in due course, but it is shocking and appalling and it’s the duty of everyone to describe it in those terms.”

He said the summit should demonstrate to Putin the “clear and united resolve” of the alliance to “stand with Ukraine and stand up to Russian aggression, whether in relation to Ukraine or whether elsewhere including cyber aggression and other ways in which Russia is aggressive around the world”.

The summit marks Starmer’s debut on the world stage and it is also an introduction for his wife Victoria to international diplomacy.

She will take part in a series of engagements with other leaders’ wives and husbands.