Benjamin Netanyahu on Thursday vowed to “harm” anyone who attacks Israel amid fears that Iran is poised to launch an unprecedented direct missile attack on its old enemy.

The Israeli prime minister said “whoever harms us, we will harm them” after US intelligence officials warned that Tehran is preparing a strike that could plunge the Middle East into a new war.

Israeli jets carried out drills simulating a strike on Iran, local media reported, while Western and Arab diplomats scrambled to persuade the Islamic republic against military action. 

Elite Iranian forces based in Syria have moved into civilian hotels in anticipation of Israeli blow-back, security sources told the Telegraph.

On Thursday, Annalena Baerbock, Germany’s foreign minister, urged “maximum restraint” in a call with her Iranian counterpart.

Senior US Republicans demanded that Joe Biden order the military to join Israel in a “devastating” response to any Iranian attack.

Iran’s Supreme Leader, Ayatollah Khamenei, has promised to take revenge for the killing of senior generals in an Israeli drone strike in Damascus in April.

Iranian state-media said the nature of the response had been decided and “punishment” would be heavy.

Tom Cotton, a Republican senator, warned that Israel was facing an “imminent” attack from Iran.

“President Biden needs to warn the Ayatollahs immediately that the United States will back Israel to the hilt and the joint American-Israeli retaliation for any attack will be swift and devastating,” Mr Cotton said.

Open warfare between Israel and Iran would be an unprecedented escalation in the conflict between Israel and Hamas, the Iranian-backed terrorist group in Gaza behind the October 7 massacre.

Rishi Sunak, the Prime Minister, said on Thursday that the “threats from Iran are completely unacceptable” and stressed that “we have always said that we will support Israel’s ability to defend itself.”

Marco Rubio, a senior Republican on the US senate intelligence committee, said the tensions marked “the most dangerous Middle East moment since 1973,” referring to the Yom Kippur war.

He added that Iran “wants to launch a large-scale attack from their own territory against Israel. Israel will respond instantly with an even more severe counterattack inside of Iran”. 

It was unclear if he had personally seen US intelligence reflecting this or was commenting on media reports.

The Telegraph understands that several senior Iranian security and intelligence officials in Damascus moved two days ago to two civilian hotels for secret military meetings, converting them into operations rooms to discuss military plans.

A security source said both hotels are hosting members of the Iranian Revolutionary Guard who work in Syria, and Iran had transferred them there to ensure their safety after last week’s attack in Damascus.

Israel has not publicly claimed responsibility for that attack on April 1, though US and Israeli officials have acknowledged it was carried out by Israel.

Ali Khamenei, the Supreme Leader of Iran, has sought to characterise that strike as an attack on Iranian territory and vowed on state TV to retaliate, though he gave no details on how that might take place. “The evil regime must be punished, and it will be punished,” he said.

On Thursday, Iranian diplomats said Tehran will soon respond to the Damascus attack, and claimed this could have been avoided had the strike been condemned by the UN Security Council.

“Had the UN Security Council condemned the Zionist regime’s reprehensible act of aggression on our diplomatic premises in Damascus and subsequently brought to justice its perpetrators, the imperative for Iran to punish this rogue regime might have been obviated,” the Iranian mission to the United Nations said on Twitter.