An Israeli airstrike on Wednesday killed at least 18 people, Palestinian officials said, at a school-turned-shelter in the Gaza Strip that Israel said Hamas used as a command post, and a United Nations agency said six of the dead were its employees.

The attack in Nuseirat, in central Gaza, came as the Israeli military resumed the offensive on another front, launching a new round of deadly raids in the occupied West Bank.

The chief U.N. relief agency for Palestinians, known as UNRWA, said the strike on the Jaouni School building in Nuseirat was the deadliest single incident for its staff over the 11 months of a war that has killed more than 200 of its workers.

The Gaza Civil Defense emergency services said that those killed included women and children, and that in addition to 18 confirmed dead, a similar number were wounded, some of them critically. It said the strike was the fifth time the school, which housed displaced people, had been hit during the war.

Gaza’s schools have not held classes since the fighting began in October, and many school buildings have become shelters for people forced to flee their homes. Israel has increasingly been targeting such schools, with analysts saying that its military has largely destroyed Hamas’s network of tunnels, forcing more fighters above ground.

Since invading Gaza after the Oct. 7 Hamas-led attack on Israel, Israeli forces have also sharply increased the frequency and intensity of raids in the West Bank, saying that it is rooting out armed militants there, as well.