Joe Biden appeared to back Sir Keir Starmer’s push for the UK to forge closer defence ties with Europe as he called the UK the “transatlantic knot” binding the two continents together.

The US President held his first face-to-face meeting with Sir Keir Starmer at the White House as Nato agreed further support for Ukraine.

The Prime Minister said the visit was an opportunity to “recommit to Nato, to recommit to the special relationship”.

The President said: “I kind of see you guys as the knot tying the transatlantic alliance together, the closer you are with Europe. We know where you are, you know where we are.”

Sir Keir wants an ambitious new UK-EU security pact to strengthen co-operation and seeks closer work on defence with key allies such as France and Germany.

The trip to the White House came less than a week from Sir Keir’s election victory and during his debut on the international leaders’ summit circuit.

Sir Keir told the president: “The special relationship is so important. It’s forged in difficult circumstances, endured for so long, and stronger now than ever.

“I’m very pleased to be able to come so early in government to recommit to Nato, to recommit to the special relationship and to discuss these affairs with you.”

A UK Government spokesman said Mr Biden and Sir Keir “agreed we must continue to do whatever it takes to support Ukraine and ensure aggressors like Putin do not win”.

The spokesman added: “The President welcomed the Prime Minister’s recent comments on establishing closer relationships with our European counterparts, as well as the UK’s commitment to Aukus.”

The meeting came as Sir Keir prepared to urge Nato allies to support Ukraine for “as long as it takes” as he confirmed the UK’s own £3 billion a year military aid for Kyiv will continue.

The Prime Minister, who met Ukraine’s President Volodymyr Zelensky in the margins of the Nato summit in Washington on Wednesday, will tell members of the alliance on Thursday that they need to send a “clear message” to Russian leader Vladimir Putin.

The UK’s military support for Ukraine will continue until at least 2030/31 and for as long as it is needed.

Sir Keir previously 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 targets in Russia.

Asked about the risk of Russian retaliation against the UK, security minister Dan Jarvis told Sky News: “Of course, we’ve got to be incredibly careful.

“But what’s most important is that in concert with our Nato allies, we work together to make sure that President Zelensky and Ukraine have got the material support they need to defend themselves against Russia.

“It is an illegal invasion, the consequences of which are massive for the whole world.”

At a special session on Ukraine at the Nato summit on Thursday, Sir Keir will warn that the frontline defence of the Euro-Atlantic region is the Ukrainian trenches.

He will say: “Nato was founded by the generation who defeated fascism. They understood not just the value of our strength, but the strength of our values.

“Those values are under attack once again. Putin needs to hear a clear message ringing out from this summit – a message of unity and determination, that we will support Ukraine with whatever it takes, for as long as it takes, to uphold our shared values and our shared security.”

The Washington summit cemented Ukraine’s “irreversible” progress towards Nato membership, with a joint statement by the allies.

But because of Nato’s Article V, which commits to mutual defence, the allies will not allow Ukraine to join while it is still at war as that would trigger an immediate conflict with Russia.

Nato allies are stepping up commitments on Ukraine while they await the results of November’s US presidential election, where Donald Trump has threatened to reduce American support.

Concerns about Mr Biden’s plan to run for re-election were evident during his Oval Office meeting with Sir Keir.

The president did not directly respond to questions about George Clooney’s criticism, after the actor and prominent Democrat supporter suggested he should leave the race.