Keir Starmer arrives in Washington to meet President Biden for the first time as Prime Minister at Nato summit amid row over Labour's defence spending plans

Sir Keir Starmer arrived in Washington today to meet US President Joe Biden and other Nato leaders at a summit to mark the alliance's 75th anniversary - amid a row over UK defence spending.

The Prime Minister and his wife Victoria touched down with their entourage at Joint Base Andrews in the early hours of the morning for his first foreign trip since taking office.

He will met the under-pressure US president and a host of other leaders including president Zelensky of Ukraine over the next two days in his first diplomatic blitz, accompanied by senior ministers.

The trip comes as Sir Keir presses for European nations to increase defence spending, but has refused to guarantee meeting his flagship commitment to hit 2.5 per cent of GDP within his first term in office, despite a 'cast iron' promise to get there.

The timescale will be set out after a wholesale defence review being launched next week - which may take a year - and must comply with the Government's strict 'fiscal rules' on spending and borrowing.

However sources told the Telegraph that the review could also look at increasing the size of the British Army, whose strength fell to a 200-year low under the Tories.

The summit is also an introduction for Lady Starmer to international diplomacy. She stayed largely out of the limelight during the election campaign but will take part in a series of engagements with other leaders' wives and husbands over the coming days.

Sir Keir will hold talks with Mr Biden in the White House this evening as the US President faces domestic pressures over his age and suitability to run for a second term.

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The prospect of Donald Trump being returned to the White House in November's election is being viewed as cause for concern within 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, Sir Keir was repeatedly pressed on whether the goal of spending 2.5 per cent of GDP would be reached within his first term.

He said: 'We are committed to the 2.5 per cent, 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 per cent 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.

Defence minister Luke Pollard told Times Radio today the Government will aim to complete the review in less than a year.

But shadow defence secretary has urged the Government to provide 'clarity'.

James Cartlidge wrote to new Defence Secretary John Healey to ask when spending would be increased.

In his letter, Mr Cartlidge said: 'Making such a clear commitment is vital for our national security.

'Our armed forces need the certainty and clarity on their funding in order to plan and prepare for the future. It is necessary to prepare everything from accommodation and benefits for service personnel to ensuring that they are equipped with the latest capabilities, equipment and technology.'

He added that it was 'high time' the Government made its plans on defence spending clear.

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

Nato members have an official goal of spending 2 per cent 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, Sir Keir acknowledged more needed to be done, particularly on locking in support for Ukraine and its president Volodymyr Zelensky, who is at the summit.

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'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,' Sir Keir told reporters.

'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.

Sir Keir 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'.

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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 Mr 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'.