At least 15 Palestinians, including eight children and two women, have been killed in an Israeli strike while queuing for nutritional supplements in front of a clinic in central Gaza, a hospital says.

Video from al-Aqsa Martyrs hospital in Deir al-Balah showed the bodies of several children and others lying on the floor as medics treated their wounds.

US-based aid group Project Hope, which runs the clinic, said the attack was a blatant violation of international law. The Israeli military said it struck a “Hamas terrorist” and regretted any harm to civilians.

They were among 66 people reportedly killed in Israeli strikes on Thursday, as Israel and Hamas continued talks on a ceasefire deal.

Despite optimism expressed by the US, which is acting as a mediator along with Qatar and Egypt, they do not so far seem to be close to a breakthrough.

Project Hope said Thursday morning’s strike in front of its Altayara health clinic in Deir al-Balah happened as patients had gathered outside, awaiting its opening to receive treatment for malnutrition, infections, chronic illnesses and more.

“Suddenly, we heard the sound of a drone approaching, and then the explosion happened,” witness Yousef al-Aydi told AFP news agency. “The ground shook beneath our feet, and everything around us turned into blood and deafening screams.”

Graphic footage posted on social media, which was verified by the BBC, showed the immediate aftermath of the attack, with adults and young children lying in a street, some severely wounded and others not moving.

At the mortuary of nearby al-Aqsa hospital, relatives of those killed wept as they wrapped the dead children in white shrouds and body bags before performing funeral prayers.

One woman told the BBC that her pregnant niece, Manal, and her daughter, Fatima, were among them, and that Manal’s son was in the intensive care unit.

“She was queuing to get the children supplements when the incident happened,” Intisar said.

Another woman standing nearby said: “For what sin were they killed?”

“We are dying before the ears and eyes of the whole world. The whole world is watching the Gaza Strip. If people aren’t killed by the Israeli army, they die trying to get aid.”

Project Hope’s president and CEO, Rabih Torbay, said the aid group’s clinics were “a place of refuge in Gaza where people bring their small children, women access pregnancy and postpartum care, people receive treatment for malnutrition, and more”.

“Yet, this morning, innocent families were mercilessly attacked as they stood in line waiting for the doors to open,” he added. “Horrified and heartbroken cannot properly communicate how we feel anymore.”

“This is a blatant violation of international humanitarian law, and a stark reminder that no-one and no place is safe in Gaza, even as ceasefire talks continue. This cannot continue.”

Unicef boss Catherine Russell said: “The killing of families trying to access life-saving aid is unconscionable.”

The Israel Defense Forces (IDF) said in a statement that it struck a member of the elite Nukhba forces of Hamas’s military wing who had taken part in the 7 October 2023 attack on Israel.

“The IDF is aware of reports regarding a number of injured individuals in the area. The incident is under review,” it added. “The IDF regrets any harm to uninvolved individuals.”

Elsewhere, five people were killed when an Israeli drone struck tents in the coastal al-Mawasi area, in southern Gaza, according to the Hamas-run Civil Defence agency.

It posted a video showing first responders recovering the bodies of three young children buried beneath sand and debris.

The attacks happened as mediators attempted to build momentum towards a ceasefire deal at indirect proximity talks in Doha.

However, significant gaps between Israel and Hamas appear to remain.

On Wednesday night, a senior Israeli official told journalists in Washington that it could take one or two weeks to reach an agreement.

The official, who was speaking during a visit to the US by Israeli Prime Minister Benjamin Netanyahu, also said that if an agreement was reached on a 60-day ceasefire, Israel would use that time to offer a permanent end to the war that would require Hamas to disarm.

On Thursday Netanyahu confirmed that “in the beginning of that ceasefire we will enter negotiations on a permanent end to the war, that is, a permanent ceasefire” and that Israel’s conditions were that Hamas must disarm and Gaza be demilitarised.

“If this can be achieved in negotiations – so much the better. If this will not be achieved in negotiations after 60 days, we will achieve it in other ways; by applying the might of our heroic army,” he said.

Netanyahu told the right-wing US media outlet Newsmax, Hamas still held 50 hostages, “20 definitely alive, and some 30 that are not alive”.

“We now have a deal that supposedly we’ll get half of the living and half of the dead out” he added, telling Newsmax “it’s been hell” for them.

Earlier, Hamas issued a statement saying that the talks had been difficult, blaming Israeli “intransigence”. The group said it had shown flexibility in agreeing to release 10 hostages, but it reiterated that it was seeking a “comprehensive” agreement that would end the Israeli offensive.

Meanwhile the EU said on Thursday said it had struck a deal with Israel to open more crossings for aid, as well as to repair infrastructure and protect aid workers.

“We count on Israel to implement every measure agreed,” EU foreign affairs chief Kaja Kallas said.

The UN said it had delivered the first fuel consignment to Gaza in four months, but warned that the 75,000 litres fell short of even a single day’s demand.

A spokesman warned that vital services would cease unless adequate fuel supplies arrived immediately.

The Israeli military launched a campaign in Gaza in response to the Hamas-led attack on southern Israel on 7 October 2023, in which about 1,200 people were killed and 251 others were taken hostage.

At least 57,762 people have been killed in Gaza since then, according to the territory’s Hamas-run health ministry.

Most of Gaza’s population has also been displaced multiple times. More than 90% of homes are estimated to be damaged or destroyed; the healthcare, water, sanitation and hygiene systems have collapsed; and there are shortages of food, fuel, medicine and shelter.