The UN Palestinian refugee agency UNRWA said six staffers were killed after two airstrikes hit a school in central Gaza on Wednesday, marking what it said was the highest death toll among its staff in a single incident.

"Among those killed was the manager of the UNRWA shelter and other team members providing assistance to displaced people," UNRWA said on X.

Earlier on Wednesday, the Israel Defence Forces said in a statement that it conducted a strike on a command and control centre in Nuseirat in central Gaza, which it said was operated by Hamas.

"This school has been hit five times since the war began. It is home to around 12,000 displaced people, mainly women and children," UNRWA said.

WATCH | Israeli airstrike killed dozens of Palestinians on Wednesday, local officials say: 

Israeli airstrike hits UN school in Gaza, officials say

Warning: This video contains an image of a dead body wrapped in a bloody shroud. Israeli airstrikes across Gaza killed dozens of Palestinians on Wednesday, local officials said, including at a UN school being used as a shelter in Al-Nuseirat refugee camp. Officials and witnesses said children were among those killed.

The Gaza government media office said the Israeli strike killed at least 18 people, including the UNRWA staff members.

U.N. Secretary-General António Guterres told Reuters on Wednesday that a lack of accountability for the killing of United Nations staff and humanitarian aid workers in Gaza was "totally unacceptable."

The Israeli military says it takes steps to reduce the risk of harm to civilians, and that at least a third of the Palestinian fatalities in Gaza are militants. It accuses Hamas of using Palestinian civilians as human shields, which Hamas denies.

The war was triggered on Oct. 7 when a Hamas-led attack on Israel killed 1,200 people and took about 250 hostages, according to Israeli tallies. Israel's subsequent assault on Gaza has killed more than 41,000 Palestinians, according to the enclave's health ministry.