Rishi Sunak will head to the Nato summit in Lithuania with a renewed call for all members of the alliance to commit to spending 2% of their gross domestic product (GDP) on defence.

The Prime Minister will tell allies in Vilnius that plans to make Nato’s armed forces “more lethal and more deployable” start with “meeting the 2% commitment”.

Downing Street said that last year, fewer than half of those in the alliance were meeting the expenditure target in relation to their national GDP — a measure of the health of an economy — with nine out of 30 members spending at least 2%.

While this is projected to rise to two-thirds of allies by 2024 — the 10th anniversary of the goal being set at the Wales summit — Government sources said Mr Sunak hoped to leave eastern Europe on Wednesday with a plan in place for all members to start meeting the target.

We cannot let the fog of war obscure the clear lessons our alliance must learn if we are going to outpace and outmanoeuvre those who seek to do us harm

No 10 said the Prime Minister will travel to Vilnius with the dual message of strengthening Nato and stressing the need to continue to support Ukraine in its war against Russia’s invading troops.

Speaking ahead of his trip, Mr Sunak said: “When thousands of Russian troops crossed the border in February last year, it marked a grim new chapter in Europe and Nato’s history.

“In the 500 days that have elapsed since, we have witnessed the most terrible crimes and human tragedies in Ukraine.

“But we have also seen the Nato alliance come together like never before in support of Ukraine and with firm determination that Russia cannot succeed.

“That is work we need to continue this week. We cannot let the fog of war obscure the clear lessons our alliance must learn if we are going to outpace and outmanoeuvre those who seek to do us harm.

“That is why the UK is investing record amounts in defence, to make our armed forces more lethal and more deployable, and to ready our defence industry for the challenges ahead.

“And that’s something we need to see across Nato — starting with meeting the 2% commitment.”

In a sign that Mr Sunak wants the UK to lead from the front, the Ministry of Defence is set to publish a new command paper setting out the measures the UK is taking to improve the “lethality and deployability of our own armed forces”, No 10 said.

The paper will include plans to establish a new Global Response Force which defence chiefs hope will dramatically increase the ability to physically respond to crises at short notice, either by being already present or deploying more rapidly.

Other issues that are expected to dominate the two-day gathering in the Lithuanian capital include Sweden’s accession to Nato, agreement on how Ukraine might eventually become a member of the alliance and the US offer to provide cluster bombs to Kyiv.

The Telegraph reported that Britain, the US, France and Germany are planning to offer “Israel-style” security guarantees to the war-torn country.

The scheme, which would involve commitments on military support and intelligence-sharing, are expected to be finalised in Kyiv in the coming days and could be offered as a stepping stone to membership, the paper reports.

Sweden and Finland dropped their long-held policy of neutrality following Russian president Vladimir Putin’s invasion of neighbouring Ukraine last year and signalled their intention to join Nato.

Finland joined in April but Turkey’s objections have held up Stockholm’s accession, although there appeared to have been a breakthrough on the eve of the summit.

The Nordic nation’s proximity to membership took a big step forward on Monday as Turkey’s President Recep Tayyip Erdogan committed to put its accession protocol before Parliament “as soon as possible” in return for help in reviving Ankara’s own chances of joining the European Union.

Ukrainian president Volodymyr Zelensky, who is due in Vilnius on Wednesday, spent last week lobbying for Nato to admit his war-torn country into Nato.

During a visit to Prague, he said the “ideal” result of the summit would be an invitation for his country to join the alliance.

A spokeswoman for Mr Sunak highlighted that, as the British leader has previously stated, he thinks Ukraine’s “rightful place is in Nato”.

But with its membership unlikely to be granted while its fight against Moscow continues – with Mr Zelensky’s troops currently engaged in counter offensive operations, Mr Sunak will push for Nato to provide long-term security assistance to Kyiv to “guarantee they can win the war”, according to his spokeswoman.

There is expected to be a diplomatic tussle over the wording of any statement released after the summit about the pace at which Kyiv might be admitted, with London calling for its membership to be fast-tracked.

Labour’s shadow defence secretary John Healey said he wanted to see Britain show leadership on “strengthening support for Ukraine” in Vilnius.

He said: “If UK military support for Ukraine is accelerated, this will have Labour’s total backing.”

Mr Sunak welcomed Joe Biden to No 10 for the first time on Monday as the US president made a layover visit to the UK on his way to the summit.

Mr Biden said the trans-Atlantic relationship is “rock solid”, while Mr Sunak hailed the US and UK as “two of the firmest allies” in Nato.

But the issue of support for Ukraine’s ambitions for Nato membership and the US decision to provide Kyiv with cluster munitions are signs that Westminster and Washington are not entirely on the same page.

Britain “discourages” their use as one of 123 signatories of a convention banning the weapons.

Separately, Conservative Party leader Mr Sunak will use day-one of his trip to confirm an eight-fold increase in the UK’s production capacity of 155mm artillery ammunition, No 10 officials said.

With most Nato armies using the ammunition as standard, a new £190 million BAE Systems contract is expected to lead to the production of more artillery shells for use by the UK and other allied forces.

No 10 said the deal would create more than 100 jobs at BAE Systems’ sites in the North of England and South Wales, adding to the firm’s existing 1,200-strong UK munitions workforce.