Israel ordered residents out of the centre of Gaza's main southern city Khan Younis and pounded the length of the enclave overnight, after the United States wielded its U.N. Security Council veto to shield its ally from a demand for a ceasefire.

Since a truce with Hamas in the two-month-old war collapsed on Dec. 1, Israel has expanded its ground assault into the southern half of the Gaza Strip, pushing into Khan Younis, where residents reported fierce battles. Both sides reported a surge in fighting in the north.

Israel said its campaign was making progress. National Security Adviser Tzachi Hanegbi said Israeli forces had killed at least 7,000 Hamas militants, without saying how that estimate was reached, and military chief Lieutenant-General Herzi Halevi told soldiers "we need to press harder".

An official toll of deaths in Gaza from the Palestinian health ministry in the Hamas-run enclave exceeded 17,700 on Saturday, with many thousands missing and presumed dead under the rubble. The ministry has said about 40% of deaths were of children under 18.

Israel launched its campaign to annihilate Gaza's Hamas rulers after their fighters burst into Israeli towns on Oct. 7, killing 1,200 people and taking 240 hostage, according to Israeli tallies.

Some 137 hostages remain in captivity, and thousands of Israelis rallied in Tel Aviv on Saturday to demand their release. A soldier who fought on Oct. 7 died from his wounds, the Israeli army said early on Sunday, adding four other soldiers died fighting in southern Gaza.

Most of Gaza's 2.3 million residents have been forced from their homes, often several times. As fighting rages across the territory, residents and U.N. agencies say there is effectively nowhere safe to go, though Israel disputes this.

Israeli forces say they are limiting civilian casualties by providing maps showing safe areas, and blame Hamas for harming civilians by hiding among them, which the fighters deny. Palestinians say the campaign has turned into a scorched-earth war of vengeance against the entire population of an enclave as densely populated as London.

Israel's Arabic-language spokesperson on Saturday posted a map on X highlighting six blocks of Khan Younis to evacuate "urgently".

Some residents reported hearing tank shelling and fierce gun battles between Israeli forces and Palestinian fighters, and a series of air strikes as Israeli forces attempted to advance further west.

"We try to put the children to sleep and we stay up fearing the place would be bombed and we'll have to run carrying the children out," said Zainab Khalil, 57, displaced with 30 relatives and friends near Jalal street where evacuations were ordered. "During the day begins another tragedy, and that is: how to feed the children?"

With food and medical supplies scarce, a senior U.N. World Food Programme official said a new system could bring more aid into Gaza through the Kerem Shalom crossing with Israel, but Israel has not yet agreed to open it.

In central Gaza, Israeli tank shelling resumed on Bureij and Maghazi refugee camps, residents said, while Palestinian health officials reported an Israeli air strike in Bureij killed seven Palestinians.

In Khan Younis, the dead and wounded arrived through the night at the overwhelmed Nasser hospital.

A medic ran out of an ambulance with the limp body of a small girl in a pink tracksuit. Inside, wounded children wailed and writhed on the tile floor as nurses raced to comfort them. Outside, bodies were lined up in white shrouds.

THOUSANDS MISSING PRESUMED DEAD

Footage obtained by Reuters inside the Jaffah hospital in Deir al-Balah showed extensive damage from a strike on a mosque next door that shuttered the medical facility.

Medical workers in northern Gaza, where some of the heaviest fighting is taking place, accused Israel of targeting hospitals and ambulances.

An ambulance worker in Gaza City's Shejaiya district, asking not to be named for fear of reprisals, told Reuters emergency crews often could not respond to calls and faced Israeli fire.

Mohammed Salha, a manager at al-Awda hospital, said Israeli forces had besieged the hospital for days with tanks, shooting people trying to enter or leave. The health ministry said Israeli forces killed two medical staffers inside Kamal Adwan hospital, also in northern Gaza, on Saturday.

An Israeli military spokesperson said it follows international law and takes "feasible precautions to mitigate civilian harm". The military has said Hamas operates from medical facilities, releasing footage to support that claim. Hamas has denied doing so.

U.S. VETO MAKES WASHINGTON 'COMPLICIT'

Israeli Prime Minister Benjamin Netanyahu on Saturday welcomed Washington's veto at the United Nations Security Council a day earlier to reject a vote backing a humanitarian ceasefire resolution, saying: "Israel will continue our just war to eliminate Hamas."

Washington has said it told Israel to do more to protect civilians but still backs Israel's position that a ceasefire would benefit Hamas. On Saturday, the Biden administration bypassed the U.S. Congress to approve an emergency sale of ammunition to Israel.

Ezzat El-Reshiq, a member of Hamas' political bureau, condemned the U.S. veto as "inhumane". Mahmoud Abbas, president of the Palestinian Authority which lost control of Gaza to Hamas in 2007, said the veto made the United States complicit in Israeli war crimes.