At least nine people were killed, including a baby, when an Israeli shell slammed into a UN-run school in the northern Gaza Strip on Thursday, an AFP correspondent said.
Emergency services spokesman Ashraf al-Qudra put the toll as high as 15 dead and dozens injured, with more bodies and wounded expected to arrive at nearby hospitals.
It was the latest in a number of Israeli strikes on schools and hospitals in the embattled Palestinian territory, as the death toll from a 17-day operation to halt rocket fire by Gaza militants topped 770.
A spokesman for the UN's Palestinian refugee agency UNRWA separately confirmed "multiple dead and injured" at the school in Beit Hanun, which was being used as a shelter by hundreds of Palestinians fleeing a major Israeli operation in the area.
"Precise coordinates of the UNRWA shelter in Beit Hanun had been formally given to the Israeli army," Chris Gunness said on his Twitter account.
AFP's correspondent saw nine bodies, including those of a one-year-old child and his mother at a morgue in nearby Beit Lahiya.
Trails and splashes of blood could be seen at the site of the shelling.
Another UN official told AFP that at around 2:50 pm (1150 GMT) a shell had landed "in or near" the school, adding that UNRWA had tried to ask people to leave shortly beforehand, fearing it might be a target.
"We were talking to the shelter asking them to leave, as we feared it was a potential target," the official said.
Gunness said there had earlier been "firing around the compound," and asked the army for time to evacuate civilians.
"We've spent much of the day trying to negotiate or to coordinate a window so that civilians, including our staff, could leave.
"That was never granted... and the consequences of that appear to be tragic," Gunness told AFP.
On Tuesday, an UNRWA school sheltering the displaced came under Israeli fire as a team was inspected damage from a day earlier.
Israel's military has also hit hospitals in Gaza, blaming resulting civilian deaths on Hamas, saying the Islamist movement uses innocents as "human shields".
UNRWA last week slammed unknown militants for storing around 20 rockets in one of its schools.
A UN official told AFP that four schools had been hit in Israel's latest operation to stamp out rocket fire from Gaza -- the bloodiest campaign since 2009.
Thirty-two Israelis soldiers have been killed in the army's ground operation, and three civilians have died in Israel from rocket fire.