At least 15 people were killed and many wounded when Israeli forces shelled a UN-run school in northern Gaza, the Gazan Ministry of Health said on Thursday.
The director of a local hospital in Gaza said various medical centers around Beit Hanoun were receiving the wounded.
The IDF said it was looking into the matter.
"Such a massacre requires more than one hospital to deal with it," said Ayman Hamdan, director of the Beit Hanoun hospital. More than 140,000 Palestinians have fled 17 days of fighting during Israel's Operation Protective Edge, many of them seeking refuge in buildings run by the UN UNWRA agency.
UN Secretary-General Ban Ki-moon said he was appalled by the attack on the school.
"Circumstances are still unclear. I strongly condemn this act," Ban said in a statement. "Many have been killed - including women and children, as well as UN staff."
Chris Gunness, spokesman for the main UN agency in Gaza UNRWA, confirmed the strike and criticized Israel.
"Precise co-ordinates of the UNRWA shelter in Beit Hanoun had been formally given to the Israeli army ... Over the course of the day UNRWA tried to coordinate with the Israeli Army a window for civilians to leave and it was never granted," Gunness said on his Twitter page.
The Palestinian death toll rose on Thursday to 729, most of whom were civilians, Gazan authorities said Thursday.
UNRWA (The United Nations Relief and Works Agency for Palestine Refugees in the Near East) has admitted to finding Hamas rockets in their facilities on two different occasions since the beginning of Operation Protective Edge 16 days ago. It said it handed them over to local authorities “answerable to the national unity government.”
In a meeting with UN Secretary- General Ban Ki-moon on Wednesday, Foreign Minister Avigdor Liberman decried that not only were rockets found in UNRWA schools in Gaza, but also that UNRWA then turned them over to Hamas, rather than to Israel.
Liberman said Israel was very “troubled” by these developments.