Israel has assassinated a senior Hamas leader in a Beirut drone strike that threatens a major escalation in the war.

Saleh al-Arouri, the deputy leader of Hamas’ political wing and commander of its militant operations in the West Bank, was among seven killed in the blast in Beirut’s southern suburbs of Daniyeh. He is the most senior member of the terror group to have been eliminated since October 7th.

A US defence official said the Israel Defense Forces (IDF) was behind the strike on a Hamas office, that also killed two members of Hamas’ militant wing.

Lebanon’s prime minister, Najib Al-Mikati said the strike was a “new Israeli crime that definitely aims to bring Lebanon into a new phase of confrontations.”

Israel did not officially confirm it was behind the attack, which struck an area of the Lebanese capital dominated by the Iran-backed terror group Hezbollah.

IDF spokesman Daniel Hagari said the military was at a “very high level of readiness” for any retaliation, while the Israeli war cabinet was due to meet on Tuesday night.

The US was not informed of the IDF operation ahead of time, Axios reported. The strike came just hours before the fourth anniversary of the American assassination of the leader of Qassem Soleimani, the leader of Iran’s Revolutionary Guard Corps external wing.

Ismail Haniyeh, Hamas’ leader, said the assassination would make the group stronger.

“All these assassinations and attacks will make us stronger and more determined than ever. This is the history of the resistance and our movement. We always become stronger and more determined,” he said in a televised speech.

Mark Regev, a senior adviser to Israeli prime minister Benjamin Netanyahu, said: “Whoever did this did a surgical strike against the Hamas leadership.

“Whoever did it must be clear - that this was not an attack on the Lebanese state,” he told MSNBC.

Thousands of Israeli troops have recently been withdrawn from Gaza, with officials briefing that some will be redeployed to the northern front on Lebanon’s border.

Israeli leaders have been drawing up plans for a war with the Iran-backed Hezbollah across that border, amid daily exchanges of artillery fire.

Iran, which funds both Hezbollah and Hamas, said Arourii’s death will “further ignite resistance against Israel” in a statement by Nasser Kanaani, the foreign ministry spokesperson.

Hezbollah has an arsenal of roughly 30,000 advanced missiles pointed at Israel.

Last month, Yoav Gallant, Israel’s defence minister, warned “If Hezbollah wants to take this up a level, we will take it up five levels.”

Arouri, 57, was closely linked to Iran and his death is a “huge loss to the Iran-Hamas relationship”, said David Makovsky, director of Arab-Israel Relations at the Washington Institute of Near-East Policy.

Western intelligence has briefed that Hezbollah and its Iranian backers do not want to provoke a wider regional war that would be difficult for them to sustain. Lebanon is suffering its worst economic crisis in history and Hezbollah knows that there is little support in the country for a war that would further devastate an already struggling nation.

Hassan Nasrallah, Hezbollah’s leader, has warned that any Israeli strike on Beirut would be met with fierce retaliation. 

On Tuesday night, a Hezbollah MP in Lebanon’s parliament vowed revenge as Hamas called for a general strike in the West Bank.

“Since Oct 7, Hezbollah has been trying hard to avoid an all-out conflict with Israel which would be catastrophic for Lebanon and them,” Maha Yahya, a Beirut-based political analyst told The Telegraph. 

“They have tried to contain the conflict along the border areas- but they also need to demonstrate that their deterrence (you bomb Beirut, we bomb Tel Aviv equation) remains meaningful.”

The Israeli military rarely confirms military operations it conducts abroad but is widely believed to have played a part in the killing of senior officials from terror groups abroad in the past. 

In 2008, Israel was involved in the assassination of Hezbollah commander Imad Mughniyeh in the Syrian capital Damascus.