The UN agency for Palestinian refugees said six of its staff members were killed when airstrikes hit a school and its surroundings in central Gaza on Wednesday.
UNRWA said this was the highest death toll among its staff in a single incident.
More than 200 UNRWA workers have been killed since the conflict between Israel and Hamas began last October.
UN Secretary-General Antonio Guterres wrote on social media on Wednesday that what’s happening in Gaza is “totally unacceptable.”
He added, “These dramatic violations of international humanitarian law need to stop now.”