Hundreds of people have been killed by an explosion at a crowded hospital in Gaza City, health officials say.
One doctor condemned what he called “a massacre” at Al-Ahli Arab Hospital, while another spoke of a scene of total devastation.
Palestinian officials say the blast was caused by an Israeli air strike.
But the Israeli military say it was the result of a failed rocket launch by Palestinian Islamic Jihad – an accusation the militant group rejected.
Israeli warplanes and artillery have been bombarding Gaza in response to an unprecedented attack on Israel on 7 October by the main Palestinian militant group, Hamas, which killed 1,400 people.
More than 3,000 people have been reported killed by strikes on Gaza.
The hospital blast is threatening efforts to resolve the humanitarian crisis there, with Jordan cancelling a planned summit on Wednesday between US President Joe Biden, King Abdullah and the Palestinian and Egyptian leaders.
Mr Biden is still travelling to Tel Aviv to show his country’s “solidarity with Israel” and “ironclad commitment to its security”.
More on Israel-Gaza war
Pictures that emerged from Al-Ahli Arab hospital on Tuesday night show scenes of chaos, with bloodied and maimed casualties being rushed out on stretchers in the darkness. Bodies and wrecked vehicles can be seen lying in the rubble-strewn street outside.
One video appears to show a projectile hitting the area followed by a blast.
“We were operating in the hospital, there was a strong explosion, and the ceiling fell on the operating room. This is a massacre,” said Dr Ghassan Abu-Sittah, a Médecins Sans Frontières plastic surgeon who had been helping to treat people wounded in the war.
Another doctor told the BBC that 80% of the hospital had been taken out of service and estimated that 1,000 people had been killed or injured.
The Ahli al-Arab hospital is fully funded by the Anglican Church, which says the facility is independent of any political factions in Gaza.
Canon Richard Sewell, the dean of St George’s College in Jerusalem and one of the Church’s top figures in the holy city, said it was difficult to get reliable information about what happened but that he could confirm the hospital had been hit and that a “horrific number of people” had died.
He told the BBC that about 6,000 displaced people had been sheltering in the hospital courtyard at the end of last week.
The hospital was first hit by an Israeli air strike that caused damage and injured four people on Saturday, he said. After that, 5,000 people left the courtyard – leaving around 1,000 remaining there, many of them invalids or elderly who needed transportation.
Revd Sewell said about 600 patients and staff treating them had been inside the hospital at the time of Monday’s explosion, but that he believed most of those killed had been outside.
“There is no justification for this type of attack, accidental or deliberate,” he added. “It is an absolute horror show which is unfolding.”
Zaher Kuhail, a British-Palestinian civil engineering consultant and university professor who was nearby at the time, told the BBC that what he had witnessed was “beyond imagination”.
“I [saw] two rockets coming from an F-16 or an F-35 [fighter jet], shelling these people and killing them ruthlessly, without any mercy,” he said.
He added that many people had been killed by fires sparked by the explosion and that first responders had lacked the equipment they needed to rescue survivors.
The health ministry in Gaza said 500 people had been killed and hundreds more were feared trapped under the rubble.
Hamas blamed an Israeli strike for what it called a “horrific massacre”.
A spokesperson for Palestinian Authority President Mahmoud Abbas, who is based in the occupied West Bank, accused Israel of a “heinous crime”.
Anger also spilled onto the streets in the West Bank. Hundreds of protesters clashed with PA security forces who responded by firing tear gas.
The Israel Defense Forces’ (IDF) first response was to stress that it did not target hospitals, and it urged caution about “unverified claims”.
Later, chief spokesman Rear Admiral Daniel Hagari said in a video statement: “Following an additional review and cross-examination of the operational and intelligence systems, it is clear that the IDF did not strike the hospital in Gaza.”
“The hospital was hit as a result of a failed rocket launched by the Islamic Jihad terrorist organisation,” he said.
He said 450 of the thousands of rockets fired indiscriminately towards Israel since the beginning of the war had fallen within Gaza, endangering civilians.
Palestinian Islamic Jihad denied that any of its rockets had been involved, saying it had not carried out any activity around Gaza City at the time.
The International Committee of the Red Cross said it was shocked and horrified by the reports.
“Hospitals should be sanctuaries to preserve human life, not scenes of death and destruction. No patient should be killed in a hospital bed. No doctors should lose their lives while trying to save others,” a statement said.
“Hospitals must be protected under international humanitarian law.”
The World Health Organization also called for the immediate protection of civilians and healthcare and urged the Israeli military to reverse the evacuation orders it has issued to 20 hospitals in northern of Gaza ahead of what is expected to be a major ground offensive.
“The order for evacuation has been impossible to carry out given the current insecurity, critical condition of many patients, and lack of ambulances, staff, health system bed capacity, and alternative shelter for those displaced.”