The Israeli missiles struck tents in an area to the west of Rafah city that was supposed to be safe from attack.
Gaza officials say the death toll from Israeli air strikes on a camp housing displaced Palestinians near Rafah in southern part of the strip has risen to 40.
“The massacre committed by the Israeli occupation army in the refugee tents northwest of Rafah city in the southern Gaza Strip has left 40 martyrs and 65 wounded,” Mohammad al-Mughayyir, a senior official at the civil defence agency, told AFP news agency.
The camp was in a designated safe zone. Witnesses said at least eight missiles struck the camp on Sunday at about 8.45pm local time (17:45 GMT).
The Wafa news agency, quoting the Palestine Red Crescent Society (PRCS), said that many of those who died were “burned alive” inside their tents in the Tal as-Sultan area.
Al Jazeera’s Sanad fact-checking agency said the attacks targeted the Brix camp to the west of the city of Rafah. An aerial photograph taken on May 24 shows hundreds of tents in the area, which was close to a UNRWA warehouse.
The Israeli attack followed Hamas’s first rocket attack on the Israeli city of Tel Aviv in months.
Israel said the eight Hamas rockets were launched from the Rafah area, where its forces have continued a ground assault despite an order from the International Court of Justice (ICJ) to halt operations there.
The Israeli military said its air force struck a Hamas compound in Rafah and that the strike was carried out with “precise ammunition and on the basis of precise intelligence”.
The attack killed Hamas’s chief of staff for the West Bank and another senior official behind deadly attacks on Israelis, it said, adding that it was “aware” of reports that “several civilians in the area were harmed” and that the incident was “under review”.
The attack led to a massive fire, which Palestinian Civil Defence teams managed to extinguish after about 45 minutes.
The International Committee of the Red Cross said its field hospital in Rafah was receiving an influx of casualties and that other hospitals also were taking in a large number of patients.
“The air strikes burnt the tents, the tents are melting and the people’s bodies are also melting,” one of the residents who arrived at the Kuwaiti Hospital in Rafah was reported as saying by the Reuters news agency.
Doctors without Borders, known by its acronym MSF, said “dozens of wounded” as well as more than 15 of the dead had been brought to a facility that it supports.
“We are horrified by this deadly event, which shows once again that nowhere is safe,” the group wrote on the social media platform X, reiterating its call for an immediate ceasefire.