Thursday's Israeli strike hit a school operated by the UN agency for Palestinian refugees, UNRWA, in the Nuseirat area of central Gaza where thousands of displaced people were sheltering.

The nearby Al-Aqsa Martyrs hospital said that at least 37 people were killed in the strike.

"Since the targeted strike the (Israeli army) has confirmed the identity of 17 terrorists that were operating from the school," the military said in a statement.

Military spokesman Rear Admiral Daniel Hagari had said Thursday nine militants were killed when fighter jets attacked three classrooms in the school.

About 30 militants from Islamic Jihad and Hamas were hiding there, he said.

UNRWA chief Philippe Lazzarini said the strike had been carried out "without prior warning".

He added that UNRWA "shares the coordinates of all its facilities (including this school) with the Israeli army and other parties in the conflict".

"Attacking, targeting or using UN buildings for military purposes are a blatant disregard of International Humanitarian law," Lazzarini said.

The bloodiest-ever Gaza war was sparked by Hamas's October 7 attack, which resulted in the deaths of 1,194 people, mostly civilians, according to an AFP tally based on Israeli official figures.

Israel's retaliatory military offensive has killed at least 36,731 people in Gaza, also mostly civilians, according to the Hamas-run territory's health ministry.