Israel's army dropped thousands of leaflets over war-torn Gaza City on Wednesday urging all residents to flee a heavy offensive through the main city of the besieged Palestinian territory.

The leaflets, addressed to "everyone in Gaza City", set out designated escape routes and warned that the urban area -- where UN humanitarian agency OCHA said up to 350,000 people were staying -- would "remain a dangerous combat zone".

The warning came as Israeli troops, backed by tanks and aircraft, have fought Hamas and Islamic Jihad militants in the heaviest combat the city has seen in months amid the war raging since October 7.

The United Nations said the latest evacuations "will only fuel mass suffering for Palestinian families, many of whom have been displaced many times".

"The civilians must be protected," said UN Secretary-General Antonio Guterres's spokesman, Stephane Dujarric.

An Israeli government spokesman said the aim was "to put civilians out of harm's way" as troops battle militants "where they are".

One woman carrying her scant belongings through the ruins, Umm Nimr al-Jamal, told AFP on Tuesday that "this is the 12th time" her family has had to flee.

"How many times can we endure this? A thousand times? Where will we end up?"

The upsurge in fighting, bombardment and displacement came as talks were to resume in Qatar towards a truce and hostage release deal in the war now grinding on into its 10th month.

Hamas official Hossam Badran, asked about the increased military operations, told AFP that Israel was "hoping that the resistance will relinquish its legitimate demands" in truce negotiations.

But "the continuation of massacres compels us to adhere to our demands", he said.

Heavy fighting also raged in Gaza's far-southern Rafah, where witnesses told AFP that Israeli tanks had rumbled into the city centre and unleashed intense fire on buildings.

'Unacceptable'

Across Gaza, deadly strikes have hit four schools used as shelters in four days, killing at least 49 people according to medics and officials in the Hamas-run territory, and sparking rebukes from France and Germany.

"It is unacceptable that schools, especially those housing civilians displaced by the fighting, should be targeted," said the French foreign ministry, urging an investigation.

Israel said the strikes had targeted militants hiding in schools.

The Israeli military concluded its operation in Gaza City's eastern district of Shujaiya, where major battles had raged since an Israeli evacuation order on June 27.

A spokesman for Gaza's civil defence agency said there was widespread "destruction".

Shujaiya has become a "ghost city", said Mahmud Bassal.

Meanwhile, an Israeli delegation led by spy chief David Barnea arrived in Doha for truce talks, said a source with knowledge of the sensitive negotiations.

CIA director William Burns was also expected in the Qatari capital after holding talks in Cairo on Tuesday.

Israel's Prime Minister Benjamin Netanyahu meanwhile met US President Joe Biden's special envoy for the Middle East, Brett McGurk.

Netanyahu "emphasised his commitment" to a proposed truce plan, "as long as Israel's red lines are preserved", his office said.

 'Stop this war'

Hamas's October 7 attack on southern Israel that sparked the war resulted in the deaths of 1,195 people, mostly civilians, according to an AFP tally based on Israeli figures.

The militants also seized 251 hostages, 116 of whom remain in Gaza, including 42 the military says are dead.

Israel responded with a military offensive that has killed at least 38,295 people in Gaza, also mostly civilians, according to figures from the territory's health ministry.

Defence Minister Yoav Gallant told Israeli lawmakers that 60 percent of Hamas fighters had been "eliminated or wounded" during the war.

Israel has imposed a punishing siege on Gaza's 2.4 million people, eased only by sporadic aid deliveries.

Medical aid group Doctors Without Borders has warned of "critical" shortages of medical supplies in Gaza, with no resupply for more than two months.

Independent UN rights experts on Tuesday accused Israel of carrying out a "targeted starvation campaign", a claim strongly rejected by Israel.

Relatives of Israeli hostages, who have piled pressure on Netanyahu demanding swift action to rescue their loved ones, began a four-day march from Tel Aviv to the seat of government in Jerusalem.

"We want all of Israel to come out with us" and "remind Netanyahu that... he needs to sign a deal to bring them back and stop this terrible war," said Ayala Metzger, daughter-in-law of hostage Yoram Metzger who died in captivity.

Since the start of the Gaza war, Israeli forces have also traded regular fire with Hezbollah militants in Lebanon, allies of Hamas, sparking fears of a broader regional conflagration.

On Wednesday, Iran-backed Hezbollah said its fighters had launched "a squadron of explosive drones" at an army base in the Israeli-annexed Golan Heights.

As the cross-border clashes have intensified, Hezbollah chief Hassan Nasrallah said Wednesday his group would end the attacks if fighting in Gaza ends.

"If a ceasefire is reached, and we all hope for that... our front will cease fire without any discussion."