White House officials believe that diplomatic efforts may be paying off in restraining Iran’s desire for revenge over the killing of Hamas leader Ismail Haniyeh in Tehran last week.

A major attack on Israel, potentially involving rockets, missiles, or drones, had been expected as early as Sunday or Monday.

However, as of Wednesday, neither Iran nor Hezbollah, the militia group it backs in Lebanon, had launched any significant military response.

Sources have told Saudi outlet Al Arabiya that the latest intelligence suggests that any attack may now be delayed until at least Thursday night or Friday.

US officials have also told CNN that Iran is still believed to be deliberating the scope of its response and that fears are now higher about Hezbollah – rather than Iran – taking the lead role.

Iran is expected to wait until after Wednesday’s meeting of the Organisation of Islamic Co-operation (OIC) in Jeddah before making a final decision, according to Al Arabiya.

Iran had requested the meeting in the aftermath of Haniyeh’s killing, which it blamed on Israel, to gain support from other governments.

The OIC said the meeting would be held in response to the “ongoing atrocities committed by the Israeli occupation against the Palestinian people, particularly in the Gaza Strip”.

In addition to the assassination of Haniyeh, the Hamas political chief, Fuad Shukr, Hezbollah’s top military commander, was killed by an Israeli airstrike in Beirut last week.

US officials believe diplomatic moves over the past week might have caused Iran to rethink its initial strategy after vowing to “punish” Israel, according to Washington Post sources.

In the wake of Haniyeh’s death, Iranian sources told The New York Times that Ayatollah Ali Khamenei, the country’s supreme leader, had issued an order to strike Israel directly

It was suggested that Iranian military commanders were considering a combined attack of drones and missiles on military targets in the vicinity of Tel Aviv and Haifa.

Another option under consideration was reportedly a coordinated attack from Iran and other fronts where it has allied forces, including Yemen, Syria and Iraq, for maximum effect.

However, it remains unclear how forcefully Iran will react and whether its attack will be designed to minimise civilian casualties and avoid escalation.

One reason why Iran could opt for a less aggressive response is the understanding that Haniyeh was killed by an explosive device planted in his room and, significantly, not a direct missile attack by Israel.

Another possible reason for Iran to delay could be the US stepping up its commitment to help defend Israel by sending extra aircrafts and war ships to the Middle East in the past week.

Benjamin Netanyahu, the Israeli prime minister, said on Wednesday that he is fully aware that his country’s citizens are on alert.

“I ask you one thing — to keep your patience and coolness,” he said. “We are prepared for both defence and offence, we are striking our enemies and are also determined to defend ourselves.”

Privately, the White House was “enraged” when Israel immediately admitted to the US that it was behind the attack that killed Haniyeh, according to reports on Wednesday.

Biden administration officials viewed the assassination as a major setback in their careful, months-long negotiations to end the war in Gaza, The Washington Post reported, citing sources briefed on the matter.

US officials were also said to be angered that Israel failed to inform them before launching other operations to assassinate other senior commanders.

‘Risk of miscalculation’

In public, Antony Blinken, the US secretary of state, repeated his call for everyone in the region to “take stock of the situation, understand the risk of miscalculation, and make decisions that will calm tensions, not exacerbate them”.

After Hassan Nasrallah, the Hezbollah chief, delivered fresh threats to the Jewish state to “prepare for any scenario” on Tuesday, Yaov Gallant, Israel’s defence minister, issued a defiant response.

Mr Gallant warned that Nasrallah may drag Lebanon “into paying extremely heavy prices”. He added: “They can’t even imagine what might happen. This may also deteriorate into a war. It’s not theoretical.”

Mr Gallant also said he held an “important” call with his German counterpart over the threats posed by Iran and its proxies, thanking Boris Pistorius “for standing with Israel”.

“The free world must come together against the biggest destabiliser and exporter of terrorism – Iran,” Mr Gallant added.

Israel Katz, the foreign minister, has accused Iran of working to smuggle weapons into Jordan to “destabilise the Jordanian regime and then flood the refugee camps” in the West Bank “with weapons and funding to establish another terror front against Israel’s major population centres”.

Evacuation of British citizens

The UK, meanwhile, has prepared for evacuation of British citizens from Lebanon, with more than 1,000 troops on standby.

As airlines continued to cancel flights to Lebanon and Israel, British ministers called for all British nationals in Lebanon to leave.

“Tensions are high, and the situation could deteriorate rapidly,” said David Lammy, the Foreign Secretary.

“While we are working round the clock to strengthen our consular presence in Lebanon, my message to British nationals there is clear – leave now.”