Sir Keir Starmer left Washington on Friday night without any announcement on allowing Ukraine to fire long-range missiles into Russia.

The Prime Minister held intensive talks with President Biden in the White House to discuss pleas from Volodymyr Zelensky to let the country use the Storm Shadow missiles.

But John Kirby, a spokesman for the US national security council, said there would be no announcement on long-range missiles after the meeting, although he did not rule out one at a later date.

Foreign Office sources had briefed against expecting the green light at the end of Starmer’s visit, but it will come as a disappointment to leave empty-handed.

On Thursday, Vladimir Putin said that permitting Western-made missiles to strike Russia would mean that Nato is engaged in “war” with Russia.

Mr Biden is reportedly holding back on supplying US-made ATACMS missiles, the country’s equivalent to the Storm Shadow, for fear of escalating the war.

But he is understood to be willing to approve the use of US intelligence and targeting systems to accompany the Storm Shadow, which is jointly produced by Britain, France and Italy.

Earlier in the week the president said he was “working on” Kyiv’s demand to use long-range missiles.

Mr Kirby suggested that Putin’s comments would not have delayed any announcement, saying they are “not something we haven’t heard before”.

But he added: “There is no change to our view on the provision of long-range strike capabilities for Ukraine to use inside Russia...for all the reasons that we said before.

“I wouldn’t be looking for an announcement today on the long range strike capabilities inside Russia,” he said.

“I can’t speak for the British and the French,” he added.

Kremlin spokesman Dmitry Peskov on Friday said Putin’s message on his ‘red line’ was unambiguous: “We have no doubt that this statement has reached its recipients.”

Russia’s UN ambassador Vassily Nebenzia warned separately that letting Ukraine use long-range weapons would plunge Nato into “direct war with... a nuclear power”.

John Bolton, a former national security advisor to Donald Trump, said he was confident Mr Biden would agree to lift restrictions on Ukraine firing Storm Shadows into Russia, if not the US-made Atacms.

“It would be extremely unusual to invite a British prime minister to the White House to say no to him. If the answer was no, that would have been delivered some other way,” he told the Telegraph.

He said the move, if it happened, was “essential” but “would have been better two and half years ago”.

Boris Johnson, the former prime minister, piled pressure on the UK and the US to allow the use of the missiles.

Speaking after a meeting with Mr Zelensky in Kyiv, he said it was “vital” that the West authorised the use of long-range missiles so Ukraine can “defend itself properly by stopping the appalling Russian attacks with glide bombs and now Iranian missiles”.

“It is obvious that they should be able to use Storm Shadow, SCALP and ATACMS as fast as possible against targets in Russia itself,” he said. “Every day that goes by means more pointless and tragic loss of Ukrainian lives.”

Grant Shapps, Britain’s former defence secretary, said the Biden-Starmer meeting “must deliver one outcome: Ukraine must be able to strike with Storm Shadows inside Russia - if Russia continues to launch attacks on Ukraine from these locations.

“This is a defining moment for supporting democracy - no more words, it’s time for the West to take real action.”

Ben Wallace, another former defence secretary, told The Telegraph long-range missiles would allow Ukraine to “layer its defence” to cover Russian attacks between 30km and 300km from the front line.

“It is a mystery to me why countries that say they want Ukraine to win, such as Germany and America, often end up in this tug of war for capabilities,” he said.

“We all know where this will end, and it’s best just to get on with it.

“Delay always benefits Russia. If we are serious about Ukraine we must make sure we remove from Russia’s grasp every factor that helps Putin now.”

In a lengthy statement posted on X, formerly Twitter, Mr Zelensky said after meeting with Foreign Secretary David Lammy and his US counterpart Antony Blinken earlier this week, “there should be no unanswered questions about why Ukraine needs sufficient long-range capabilities.

“When we ask for these systems, we repeatedly hear ‘We are working on it’.

”I am grateful to those who made the commitments and are fulfilling them, but we are still far from fully implementing what has been agreed.

“It’s difficult to repeatedly hear ‘We are working on this’, while Putin continues to burn down our cities and villages.”

Mr Putin said allowing long-range strikes “would mean that Nato countries, the United States, and European countries are at war with Russia... if this is so, then, bearing in mind the change in the very essence of this conflict, we will make appropriate decisions based on the threats that will be created for us”.

Earlier this week, Mr Lammy and Mr Blinken announced further financial support for Ukraine, including a £600 million package from the UK and $717 million (£550 million) from the US to meet immediate humanitarian, energy and stabilisation.