The head of Israel’s foreign intelligence service has vowed to track down and kill all Hamas leaders responsible for attacking Israel, less than a day after a drone strike in Lebanon killed the militant organisation’s second most senior official. David Barnea said on Wednesday the Mossad was “committed to settling the score with the murderers who descended upon the Gaza envelope” on 7 October and with those who planned the attacks. Barnea spoke at the funeral of the former Mossad director Zvi Zamir, who oversaw Israel’s bloody retaliation against Palestinian militant groups after the 1972 killings of Israeli Olympic athletes in Munich. “It will take time, just like after the Munich massacre, but we will lay our hands on them wherever they will be … Every Arab mother ought know that if her son participated, directly or indirectly, in the slaughter of 7 October, his blood shall be upon his own head,” Barnea told mourners. Israel has not formally accepted responsibility for the strike in a southern Beirut suburb that killed Saleh al-Arouri, the deputy political chief of Hamas. In recent months, Israeli officials have pledged a repeat of the campaign launched after Munich, which led to more than a dozen assassinations in European countries, north Africa and Lebanon. Both Benjamin Netanyahu, the Israeli prime minister, and Ronen Bar, the head of the Shin Bet, the internal security service, have promised the public and parliamentarians to hunt down Hamas leaders overseas. Israel has waged a nearly three-month war against Hamas in Gaza after the Palestinian militant group launched the 7 October attack on southern Israel that resulted in the deaths of at least 1,200 people, mostly civilians. The offensive launched by Israel in Gaza after the attack has since killed at least 22,313 Palestinians there, according to the health ministry in the Hamas-run territory. Hamas officials expressed defiance after the assassination of Arouri, 58. “We say to the criminal occupation [Israel] that the battle between us is open,” said Husam Badran, a member of Hamas’s politburo. Ismail Haniyeh, the leader of Hamas, said the organisation was “more powerful and determined” after the strike, which killed six other Hamas officials. The assassination has increased fears of a major outbreak of violence on Israel’s northern border. Hezbollah, a heavily-armed Islamist militant movement based in Lebanon that is loosely allied with Hamas, has been exchanging near-daily fire with Israel across the border since the war in Gaza began. More than 100 Hezbollah fighters and two dozen civilians have been killed on Lebanese territory in the violence, as well as at least nine Israeli soldiers in Israel. In a much anticipated televised speech on Wednesday, Hasran Nasrallah, the leader of Hezbollah, called the assassination of Arouri a “heinous crime” that “will not go unanswered or unpunished” but stopped short of announcing an immediate escalation of hostilities. Nasrallah claimed Hezbollah had already deterred an Israeli invasion of Lebanon and was not afraid of war. “We are not intimidated …. If you are considering war with us you will regret it,” Nasrallah said, adding that he would give further details of Hezbollah’s response to the assassination of Arouri in a second speech on Friday. Kandice Ardiel, a spokesperson for the UN interim force in Lebanon (Unifil), which was deployed to the south of Lebanon in 1978 in an effort to prevent conflict between militants there and Israel, said UN officials were deeply concerned at any potential for escalation that could have devastating consequences for people on both sides of the border. “We continue to implore all parties to cease their fire, and any interlocutors with influence to urge restraint,” she said. Arouri, who was killed in a neighbourhood that is a Hezbollah stronghold in Beirut, is the first senior Hamas leader to die since 7 October. Analysts say it is difficult to predict how Hezbollah will respond. Nasrallah, who has led Hezbollah since an Israeli strike killed his predecessor in 1992, has appeared reluctant to escalate the current level of clashes, perhaps fearing a repeat of the month-long 2006 war in which Israel heavily bombed Beirut and southern Lebanon. His decision will depend on the views of senior leaders in Tehran. Iran guided the foundation of Hezbollah in the aftermath of Israel’s 1982 invasion of Lebanon and has remained an influential sponsor. Iran’s often bellicose rhetoric may not be matched by action, some analysts suggest, as Tehran now sees Hezbollah’s primary role as providing a threat of retaliation if Israel should strike Iran directly. Iranian officials would therefore be reluctant to risk the most potent member of the “axis of resistance” they have built up across the region in a major war. “I don’t think Hezbollah will be willing to drag Lebanon into a major conflict at this particular moment and time given the situation regionally,” said Maha Yahya of the Carnegie Middle East Center thinktank. Israeli officials have warned in recent weeks of action against Hezbollah unless its cross-border fire stops. Tens of thousands of Israelis remain displaced from their homes along the border with Lebanon for fear of bombardment or a raid. Military spokespeople said Israeli forces were prepared for any scenario, and Israeli national radio reported the deployment of additional Iron Dome anti-missile batteries. The US state department said that American officials were monitoring the situation closely. The secretary of state, Antony Blinken, is due to visit Israel next week. Observers warn the killing of Arouri is further evidence the war between Israel and Hamas is spreading across the region. Violence involving other militant groups in the Iran-led “axis of resistance” has flared in recent weeks with Houthi rebels attacking cargo vessels in the Red Sea, a key shipping lane for world trade. On Wednesday, the US, UK, Australia and nine other countries warned of unspecified consequences unless the Houthis halt such attacks, but it was unclear what impact such calls would have. There has been violence, too, in Syria, Iraq and in the occupied West Bank – the Palestinian territory where Arouri was born. Hundreds of Palestinians took to the streets of Ramallah and other towns in the West Bank to condemn his killing, chanting “revenge, revenge”, and the Palestinian Authority called a general strike to mourn his death. In Israel, the assassination was widely welcomed. A headline in the Israel Hayom local newspaper called Arouri a “mass murderer” and hailed “an appropriate end for the man responsible for countless terrorist attacks”. In the mass-market Yedioth Ahronoth newspaper, the columnist Nahum Barnea wrote that Arouri “earned his well-deserved spot” on Israel’s hitlist. With Israeli military casualties mounting, resistance continuing and the most senior Hamas leaders still unharmed, Israeli officials have been under increasing pressure to show results to boost domestic morale. Netanyahu has vowed to press ahead with the assault in Gaza until Hamas is destroyed and the more than 100 hostages taken on 7 October and still held by the militant group in Gaza are freed. The campaign has driven about 85% of Gaza’s population from their homes, forcing hundreds of thousands of people into overcrowded shelters or teeming tent camps in Israeli-designated safe areas that the military has nevertheless bombed. Israel’s siege of the territory has left a quarter of Gaza residents facing starvation, according to the UN. Palestinians reported heavy airstrikes and artillery shelling in the southern city of Khan Younis and farming areas to the east. The Palestinian Red Crescent said Israel bombed its headquarters in the city, killing five people, and after a strike on the Nuseirat refugee camp in central Gaza on Tuesday Palestinians rushed to rescue victims and retrieve bodies from the rubble. “There are about 12 martyrs so far, mostly children,” said a bereaved resident, Ghazi Darwish. “What was their fault? Among them my one-month-old son, what did he do to Israel? My other son is five years old, he was also martyred.” Further south in Khan Younis, the Palestinian Red Crescent said Israel had twice struck its headquarters, killing five people, on Tuesday. The head of the World Health Organization, Tedros Adhanom Ghebreyesus, deplored the strikes as “unconscionable” and said “Gaza’s health system is already on its knees”.