At least 54 Palestinians have been killed in two separate Israeli air strikes overnight, including a strike on a school sheltering displaced families in central Gaza, two hospital directors have told the BBC.

Fahmi Al-Jargawi School in Gaza City had been housing hundreds of displaced people from the town of Beit Lahia, currently under intense Israeli military assault.

A spokesperson for Gaza's Hamas-run Civil Defence said 20 bodies, including those of children, were recovered – many were severely burned, after fires engulfed two classrooms turned into living quarters.

The Israeli military (IDF) said it had targeted "a Hamas and Islamic Jihad command and control centre".

The IDF said the area was being used "by the terrorists to plan... attacks against Israeli civilians and IDF troops", and accused Hamas of using "the Gazan population as human shields".

"Flames were everywhere. I saw charred bodies lying on the ground," said Rami Rafiq, a resident living across from the school, in a phone call with BBC. "My son fainted when he saw the horrific scene."

Video footage shared online showed large fires consuming parts of the school, with graphic images of severely burned victims, including children, and survivors suffering critical injuries.

Local reports said among the dead was Mohammad Al-Kasih, the head of investigations for the Hamas police in northern Gaza, along with his wife and children.

Separately, a strike on a house in Jabalia in northern Gaza killed 19 people, according to the director of al-Ahli hospital Dr Fadel el-Naim. The Israeli military has not yet commented on what was being targeted.

The twin attacks are part of a broader Israeli offensive that has escalated in the northern part of the enclave over the past week.

The IDF said it hit 200 targets across Gaza in 48 hours as it continued its operations against what it called "terrorist organisations".

On Friday, an Israeli strike on the home of a Palestinian doctor in Gaza killed nine of her 10 children. Dr Alaa al-Najjar's 11-year-old son was injured, along with her husband, Hamdi al-Najjar, who is in critical condition.

The nine children - Yahya, Rakan, Raslan, Gebran, Eve, Rival, Sayden, Luqman and Sidra - were aged between just a few months old and 12. The Israeli military has said the incident is under review.

Meanwhile, the Red Cross said two of its staff were killed in a strike on their home in Khan Younis on Saturday.

The killing of Ibrahim Eid, a weapon contamination officer, and Ahmad Abu Hilal, a security guard at the Red Cross Field Hospital in Rafah "points to the intolerable civilian death toll in Gaza", the ICRC said, repeating its call for a ceasefire.

On Sunday, the head of a controversial US and Israeli-approved organisation that sought to use private firms to deliver aid to Gaza resigned.

In a statement by the Gaza Humanitarian Foundation (GHF), executive director Jake Wood said it had become apparent that plans to set up distribution hubs would not meet the "humanitarian principles" of independence and neutrality.

The GHF said in response that it was disappointed at his resignation, but insisted it would "begin direct aid delivery in Gaza" on Monday.

"Our trucks are loaded and ready to go," it said in a statement, adding that the new aid operation would reach "over one million Palestinians by the end of the week" and that there were plans to "scale rapidly to serve the full population in the weeks ahead".

Israel imposed a total blockade on Gaza on 2 March that lasted 11 weeks before it allowed limited aid to enter the territory in the face of warnings of famine and mounting international outrage.

Israeli military body Cogat said on Saturday morning that 388 trucks carrying aid had entered Gaza since Monday. The UN says much more aid - between 500 to 600 trucks a day - is needed.

Meanwhile, 20 countries and organisations met in Madrid on Sunday to discuss ending the war in Gaza. Spanish Foreign Minister Jose Manuel Albares called for an arms embargo on Israel if it did not stop its attacks.

Israel launched a military campaign in Gaza in response to Hamas's cross-border attack on 7 October 2023, in which about 1,200 people were killed and 251 others were taken hostage.

At least 53,939 people, including at least 16,500 children, have been killed in Gaza since then, according to the territory's health ministry.