The naming of Sinwar to lead the Palestinian group came as Israel steeled itself for potential Iranian retaliation over the assassination of his predecessor Ismail Haniyeh last week in Tehran.

Speaking at a military base on Wednesday, Prime Minister Benjamin Netanyahu said Israel was "determined" to defend itself.

"We are prepared both defensively and offensively," he told new recruits.

Army chief Herzi Halevi vowed to "find him (Sinwar), attack him" and force Hamas to find someone to replace him.

Sinwar -- Hamas's leader in Gaza since 2017 -- has not been seen since October 7 operation.

A senior Hamas official told AFP Sinwar's selection sent a message that the organisation "continues its path of resistance".

Analysts believe Sinwar has been both more reluctant to agree to a Gaza ceasefire and closer to Tehran than Haniyeh, who lived in Qatar.

"If a ceasefire deal seemed unlikely upon Haniyeh's death, it is even less likely under Sinwar," said Rita Katz, executive director of the SITE Intelligence Group, adding Hamas would "only lean further into its hardline militant strategy".

US Secretary of State Antony Blinken has said it is up to Sinwar to help achieve a ceasefire, saying he "has been and remains the primary decider".

 Hezbollah vows response

In Lebanon, Hezbollah has also pledged to avenge the assassinations of Haniyeh and its own military commander Fuad Shukr in an Israeli strike in Beirut.

In a televised address to mark one week since Shukr's death, Hezbollah leader Hassan Nasrallah said Tuesday his group would retaliate "alone or in the context of a unified response from all the axis" in the region.

The United States, which has sent extra warships and jets to the region, has urged both Iran and Israel to avoid an escalation.

President Joe Biden this week spoke with regional leaders, while Blinken told reporters the message of restraint had also been communicated "directly" to both Israel and Iran.

French President Emmanuel Macron told Netanyahu on Wednesday to "avoid a cycle of reprisals", after earlier delivering the same message to his Iranian counterpart Masoud Pezeshkian, the French presidency said.

Pezeshkian told Macron in a separate telephone call that the West "should immediately stop selling arms and supporting" Israel if it wanted to prevent war, his office said.

Hezbollah has traded near-daily cross-border fire with Israeli troops throughout the Gaza war.

On Wednesday, a Lebanese security source said that a Hezbollah fighter and a civilian were killed in an Israeli strike near Jouaiyya close to the border. The Israeli military said it had eliminated a Hamas commander in the area.

The Israeli army later said its jets had destroyed a launcher on Wednesday night that had been used by Hezbollah to send drones towards the occupied Golan Heights earlier in the evening.

Numerous airlines have suspended flights to Lebanon or limited them to daylight hours due to security fears, while Egypt said Iran had warned civilian airlines to steer clear of its airspace as it will be conducting military exercises overnight.

The United Nations said it was "temporarily" reducing the presence of UN staff family members in Lebanon, although it was not moving its staff.

Israel's occupation army said early Thursday that a strike in Gaza late last month had killed senior Hamas member Nael Sakhl, whom it said was involved in directing activities in the occupied West Bank.

The war has created a humanitarian crisis in Gaza, with almost all of its 2.4 million people displaced and suffering from food shortages.

Israel's far-right Finance Minister Bezalel Smotrich drew sharp condemnation from some allies on Wednesday for suggesting that "it might be justified" to starve the besieged territory.

"No one in the world will allow us to starve two million people, even though it might be justified and moral," he said at a conference earlier this week.

The EU said Smotrich's remarks showed "contempt for international law and for basic principles of humanity".

France expressed its "deep dismay" at the comments, while UK Foreign Minister David Lammy called on "the wider Israeli government to retract and condemn them".