Smoke and debris rises over Gaza, amid the ongoing conflict between Israel and Hamas. Reuters

Israel bombed Gaza on Thursday as a top White House advisor was due to arrive in Jerusalem with a rift growing over US calls for its ally to exercise restraint.

It has left besieged Gaza in ruins, killing more than 18,600 people, mostly women and children, according to the Hamas-run health ministry, and devastating homes, roads, schools and hospitals.

The ministry said Israeli air strikes early on Thursday had killed at least 19 people across the Gaza Strip.

US President Joe Biden, whose government has provided billions of dollars in military aid to Israel, on Wednesday gave his sharpest rebuke of the war yet, saying Israel's "indiscriminate bombing" of Gaza was weakening international support.

But Israeli Prime Minister Benjamin Netanyahu doubled down on his offensive, vowing "we are going until the end, until victory, nothing less than that".

And Foreign Minister Eli Cohen said the war against Hamas would continue "with or without international support".

On Thursday, Biden's National Security Advisor Jake Sullivan was due to arrive in Jerusalem for talks with Netanyahu and his war cabinet.

US President Joe Biden speaks during a press conference. File photo

Sullivan told a Wall Street Journal event ahead of his trip he would discuss a timetable to end the war and urge Israeli leaders "to move to a different phase from the kind of high-intensity operations that we see today".

Netanyahu has said there is also "disagreement" with Washington over how a post-conflict Gaza would be governed.

Hamas chief Ismail Haniyeh said on Wednesday "any arrangement in Gaza or in the Palestinian cause without Hamas or the resistance factions is a delusion".

He said Hamas was ready for talks that could lead to a "political path that secures the right of the Palestinian people to their independent state with Jerusalem as its capital".

'Darkest chapter'

Diplomatic pressure is mounting on Israel to better protect civilians, with the UN General Assembly this week overwhelmingly backing a non-binding resolution for a ceasefire.

While Washington voted against, allies Australia, Canada and New Zealand, who, in a rare joint statement, said they were “alarmed at the diminishing safe space for civilians in Gaza, supported the resolution".

Palestinian children injured following Israeli strikes receive care at Al-Aqsa hospital on Monday. AFP

CNN reported on Wednesday citing US intelligence that nearly half of the air-to-ground munitions used by Israel in Gaza since October 7 have been unguided, which can pose a greater threat to civilians.

The head of the UN agency for Palestinian refugees, Philippe Lazzarini, said on Wednesday that Gazans were "facing the darkest chapter of their history".

Wintry rain lashed the territory, where the UN estimates 1.9 million of Gaza's 2.4 million population have been displaced, living in makeshift tents as supplies of food, drinking water, medicines and fuel run low.

Ameen Edwan said his family was camped out with thousands in the grounds of the Al-Aqsa Martyrs hospital in central Gaza.

"Rainwater seeped in. We couldn't sleep. We tried to find nylon covers but couldn't find any, so we resorted to stones and sand" to keep the water out, he said.

The southern city of Rafah near the Egyptian border has become a vast camp for the displaced, with hundreds of tents erected using wood and plastic sheets.

"We spent five days outdoors. And now the rain has flooded the tents," said a displaced resident, Bilal al-Qassas.

Gusts of wind shook the fragile structures, while people tried to reinforce them with more plastic sheeting.

"Where do we migrate to? Our dignity is gone. Where do women relieve themselves? There are no bathrooms," said 41-year-old Qassas.

US ambassador to the UN Linda Thomas-Greenfield speaks to delegates during the UNGA in New York. Reuters

The UN warned the spread of diseases -- including meningitis, jaundice and upper respiratory tract infections -- had intensified.

Gaza's hospital system is in ruins, and Hamas authorities said vaccines for children had run out, warning of "catastrophic health repercussions".

The Hamas-controlled health ministry said Israeli forces opened fire on wards of Kamal Adwan hospital in north Gaza.

The army has yet to comment, but Israel has repeatedly accused Hamas of using hospitals, schools, mosques and vast tunnel systems beneath them as military bases -- charges it denies.

Growing troop toll

In Israel, the army is coming under growing pressure to limit troop deaths and secure the release of hostages.

It has lost 115 soldiers, including 10 on Tuesday, its deadliest day since the ground assault began on October 27.

In the October 7 attack — the deadliest in Israel's 75-year history — Hamas also seized around 240 hostages.

Palestinians mourn relatives killed in the Israeli bombardment of the Gaza Strip outside a morgue in Khan Younis. AP

Hamas released dozens of hostages in exchange for Palestinian prisoners held by Israel during a week-long truce last month, but others have been found dead.

Families of hostages said Wednesday they had demanded "an immediate explanation from the Prime Minister and cabinet members" after local media reported that the government had rejected a proposal to send officials to Qatar for a second round of hostage negotiations.

Israel's embassy in Romania on Wednesday announced the death of Israeli-Romanian Tal Haimi, 41, who was held in Gaza.

Washington and London announced further sanctions Wednesday against Hamas, targeting "key officials who perpetuate Hamas's violent agenda".

Fears of the conflict broadening remain, with daily incidents along Israel's border with Lebanon, where Iran-backed Hezbollah is based.

Agence France-Presse