Heavy fighting raged in central and southern Gaza on Wednesday as fears mounted of a regional escalation following a strike in Beirut that killed one of the top Hamas leaders.

The strike was widely blamed on Israel but its implications for the war remain unclear.

Israeli officials have not commented on the attack on Tuesday that killed Saleh Arouri, the most senior Hamas member to die since the war in Gaza erupted nearly three months ago.

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Top Hamas political leader Saleh Arouri was killed in an apparent Israeli strike on an apartment building in a Beirut suburb that is a Hezbollah stronghold (Hussein Malla/AP)

Israel has killed several top Hamas leaders over the years, only to see them quickly replaced.

And the strike in Hezbollah’s southern Beirut stronghold could cause the low-intensity fighting along the Lebanon border to boil over into all-out war.

Much depends on how Hassan Nasrallah – who has led Hezbollah since an Israeli strike killed his predecessor in 1992 – chooses to respond. He has previously vowed to retaliate for any Israeli targeting of allied militant leaders in Lebanon, and is expected to deliver a speech at 6pm local time (1600 GMT).

Hezbollah and the Israeli military have been exchanging fire almost daily over the Israeli-Lebanese border since the war in Gaza began, but Nasrallah has appeared reluctant to escalate it further, perhaps fearing a repeat of the month-long 2006 war, in which Israel heavily bombed Beirut and southern Lebanon.

Israeli officials have not commented on the strike that killed Arouri, but Rear Admiral Daniel Hagari, an Israeli military spokesman, said “we are on high readiness for any scenario”.

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Hezbollah civil defence workers search for remains near an apartment building in Beirut where Hamas leader Saleh Arouri was killed in an apparent Israeli strike (Hussein Malla/AP)

The United States has sought to prevent any widening of the conflict, including by deploying two aircraft carriers and other military assets to the region. Secretary of State Antony Blinken is expected in the region this week.

Israeli Prime Minister Benjamin Netanyahu and other officials have repeatedly threatened to kill Hamas leaders wherever they are. The group’s October 7 attack from Gaza into southern Israel killed around 1,200 people, and some 240 others were taken hostage.

Israel claims to have killed a number of mid-level Hamas leaders in Gaza, but this would be the first time since the war that it has reached into another country to target the group’s top leaders, many of whom live in exile around the region.

Arouri was the deputy of Hamas’s supreme political leader, Ismail Haniyeh, and headed the group’s presence in the Israeli-occupied West Bank. He was also a key liaison with Hezbollah.

The US State Department had listed him as a terrorist and offered a 5 million dollar (£4 million) reward for information about him.

Haniyeh said Hamas is “more powerful and determined” following the attack, which killed six other members of the group, including two military commanders.

“They left behind them strong men who will carry the banner after them,” he said of those killed.

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Palestinians look at the destruction after an Israeli strike in Rafah, in the southern Gaza Strip (Fatima Shbair/AP)

Hezbollah called the strike “a serious attack on Lebanon, its people, its security, sovereignty and resistance”.

“We affirm that this crime will never pass without response and punishment,” it said.

Meanwhile, the focus of the war remains on Gaza, where Israeli Defence Minister Yoav Gallant said Israel is seeking a “clear victory” over Hamas, which has ruled the territory since 2007.

Israel’s air, ground and sea assault in Gaza has killed more than 22,300 people, two-thirds of them women and children, according to the Health Ministry in the Hamas-ruled territory. The count does not differentiate between civilians and combatants.

The campaign has driven some 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.

A quarter of Gaza’s population face starvation, according to the United Nations, as Israeli restrictions and heavy fighting hinder aid delivery.

The unprecedented death and destruction has led South Africa to accuse Israel of genocide in a case filed with the International Court of Justice, allegations that Israel has strongly denied and vowed to contest.

Nevertheless, Israel appears far from achieving its goals of crushing Hamas and returning the estimated 129 hostages still held by the group after more than 100 were released in a ceasefire deal in November.

Mr Gallant said several thousand Hamas fighters remain in northern Gaza, where Israeli troops have been battling militants for more than two months and where entire neighbourhoods have been blasted into rubble.

Heavy fighting is also under way in central Gaza and the southern city of Khan Younis, where Israeli officials say Hamas’s military structure is still largely intact. Yehya Sinwar, Hamas’s top leader in Gaza, and his deputies have thus far eluded Israeli forces.

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A house destroyed by an Israeli air strike on Khan Younis on Sunday (Mohammed Dahman/AP)

Egypt, which along with Qatar has served as a mediator between Israel and Hamas, has proposed a multistage plan for ending the war in which all hostages would eventually be released in exchange for Palestinians imprisoned by Israel.

Israel would withdraw from Gaza and a government of Palestinian technocrats would govern Gaza and parts of the occupied West Bank until elections are held.

Neither Israel nor Hamas have accepted the plan in its entirety, but neither has rejected it outright.

An Israeli delegation was in Cairo on Wednesday to discuss the proposal, according to an Egyptian official, but he added that the killing of Arouri is likely to hamper the negotiations for a couple days.