"Humanitarian aid workers must never be victims of rockets," the foreign ministry said on social media platform X. "The death of six UNRWA staff at a school in Nuseirat is totally unacceptable."

Israel on Wednesday bombed a school housing displaced Palestinians in Nuseirat, central Gaza, which rescuers said killed 18 people, including UN staffers.

The UN agency for Palestinian refugees UNRWA later said six of its staffers had been killed in two Israeli air raids on the Nuseirat school and its surroundings.

The German foreign ministry said that "UNRWA is providing vital aid in Gaza and has a UN mandate to do so. Israel's army has a responsibility to protect UN staff and aid workers."