The US-led diplomatic effort to avert war remains intense, with Antony Blinken, the secretary of state, expected to arrive in the region on Tuesday night.

Sir Keir Starmer, the Prime Minister, and Olaf Sholtz, the German chancellor, spoke to Masoud Pezeshkian, Iran’s president, on Monday, expressing their concern about a regional war if Iran followed through on its threats to attack Israel directly.

The US, Britain, France, Italy and Germany urged Tehran to stand down in a joint letter.

However, Iran continued to insist on its right to respond to an attack on its soil.

Nasser Kanaani, the spokesman for the Iranian ministry of foreign affairs, said: “The declaration by France, Germany and Britain, which raised no objection to crimes of the Zionist regime, brazenly asks Iran to take no deterrent action against a regime which has violated its sovereignty.”

Instead of issuing such demands, Western nations should “once and for all stand up against the war in Gaza and the warmongering of Israel”, Mr Kanaani added.