Joe Biden is poised to allow Ukraine to fire Storm Shadow missiles inside Russia for the first time.

Mr Biden is expected to give his blessings for the British-made weapon to be used in Kursk, after authorising similar American long-range missiles to be deployed.

Olaf Scholz, the German chancellor, is now under increasing pressure to allow Taurus missiles to join the offensive, which would give Ukraine a trio of new munitions to hit high-value Russian targets.

British and American officials declined to comment on private conversations about the missiles on Monday, citing the risk that Russia could move its resources out of range before the weapons could be deployed.

But Sir Keir Starmer, the British Prime Minister, said at the G20 summit in Rio de Janeiro that Ukraine’s Western supporters must “double down”, after Vladimir Putin sent North Korean troops into Kursk to fight off Kyiv’s advance into Russian territory.

He said: “We need to make sure Ukraine has what is necessary for as long as necessary, because we cannot allow Putin to win this war.”