Twenty-one Palestinians died after gas fired into the crowd caused a crush at an aid distribution centre in Khan Younis in southern Gaza on Wednesday, the enclave's Health Ministry said.
Fifteen of those killed died by suffocation, the ministry added. The Gaza government media office said that six others were shot dead.
“This is the first time deaths have been recorded due to suffocation and severe crowd crush at the aid distribution centres,” the ministry said.
It accused Israel and the Gaza Humanitarian Foundation of “deliberately and systematically committing massacres in various ways against hungry people”.
The Gaza media office said the GHF invited hundreds of people to receive the aid at the centre and then deliberately closed the gates with them inside.
"The employees of the foundation and the Israeli soldiers sprayed the pepper gas and fired at the hungry people," the office said. "This led to mass suffocation and the death of this large number of martyrs and the injury of scores due to the crush in a closed place."
The office reported witness accounts from 14 people who were at the scene.
Earlier in the day, the US and Israel-backed aid GHF said that 20 people were killed in the incident, in what it described as a crowd surge caused by armed men.
“Our current understanding is that 19 of the victims were trampled and one was stabbed amid a chaotic and dangerous surge, driven by agitators in the crowd,” the GHF said.
The group said that it had “credible reason to believe that elements within the crowd – armed and affiliated with Hamas – deliberately fomented the unrest”.
Several people were identified as having guns in the crowd, one of which was confiscated, the group said.
An American worker was also threatened with a firearm by a member of the crowd during the incident, the group added.
The Gaza media office has rejected the GHF's claims, saying that its attempts to blame innocent people or Palestinian factions is "aimed only at evading legal, moral and human responsibility".
The GHF has been mired in controversy since its inception for numerous incidents in which hundreds of Palestinians have been killed. US contractors working with the aid group and the Israeli army have been accused of firing at hungry Palestinian gathering to receive aid supplies at the centres.
Israeli soldiers and officials allege they were given orders to deliberately shoot Palestinians near the GHF sites, according to a report published by Israeli newspaper Haaretz last month.
The group has repeatedly denied incidents have occurred at its sites and has accused the UN of spreading misinformation, an accusation the UN denies.
The UN rights office said on Tuesday it had recorded at least 875 killings in the past six weeks at aid points in Gaza run by the GHF and convoys run by other relief groups, including the UN.
The majority of those killed – 674 – were in the vicinity of GHF sites, while the remaining 201 were killed on the routes of other aid convoys, the rights office said.
The GHF uses private US security and logistics companies to get supplies into Gaza, largely bypassing a UN-led system that Israel alleges has let Hamas militants loot aid shipments intended for civilians. Hamas denies the allegation.
The UN has called the GHF aid model “inherently unsafe” and a violation of humanitarian impartiality standards.
The GHF said on Tuesday it had delivered more than 75 million meals to Palestinians since the end of May, and that other humanitarian groups had “nearly all of their aid looted” by Hamas or criminal gangs.
The UN Office for the Co-ordination of Humanitarian Affairs has previously cited instances of violent pillaging of aid, and the UN World Food Programme said last week that most lorries carrying food assistance into Gaza had been intercepted by “hungry civilian communities”.
The EU's foreign policy chief Kaja Kallas said on Tuesday that Israel needs to take more concrete steps to improve the humanitarian situation in Gaza and fully implement the agreement it made with the EU last week.
“Israel needs to take more concrete steps to improve the humanitarian situation on the ground. The European Union will keep a close watch,” Ms Kallas said after meeting EU foreign ministers in Brussels.
