Israel's army dropped thousands of leaflets over war-torn Gaza City 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, which had a pre-war population of over half a million, would "remain a dangerous combat zone".

Elsewhere across Gaza, deadly strikes have hit four schools used as shelters in four days, sparking rebukes from France and Germany which both labelled the attacks "unacceptable".

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

The health ministry in Hamas-run Gaza said Wednesday at least 38,295 people have been killed in the war.

The toll added 52 new deaths in 24 hours, a ministry statement said. It said 88,241 people have been wounded.

The latest fighting in Gaza has newly displaced 350,000 civilians, said UNRWA chief Philippe Lazzarini, who spoke before the leaflet drop and said "there is absolutely no safe space in Gaza".

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

An Israeli delegation led by Mossad chief David Barnea arrived in Doha, a source with knowledge of the negotiations said, speaking on condition of anonymity.

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

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

The Israeli army said it was reviewing the Khan Yunis area attack Tuesday in which hospital sources said at least 29 people were killed in a school used as a displacement shelter.

Gaza's Hamas government said a "majority" of the dead were women and children.

Three previous strikes since Saturday on Gaza schools used by displaced Palestinians have killed a total of at least 20 people, said Gaza officials and rescue services.

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.