US Secretary of State Antony Blinken called Thursday for the protection of aid workers after UN staffers were killed in Gaza.

Ane he argued that a US-backed ceasefire was the best way to ensure their safety.

"We need to see humanitarian sites protected, and that's something that we continue to raise with Israel," Blinken told reporters on a visit to Poland.

Blinken, however, also said that Hamas -- at war with Israel since its October 7 attack -- bore some responsibility.

"We continue to see Hamas hiding in, taking over, and otherwise using these sites from which to conduct its operations," Blinken said.

The UN agency for Palestinian refugees UNRWA said six of its staffers had been killed in two Israeli air raids on the Nuseirat school and its surroundings, drawing statements of outrage around the world.

"I think it also underscores, once again, the urgency of reaching a ceasefire," Blinken said.

Blinken, who has been pushing for a truce deal for weeks.

A ceasefire was "the best way of ensuring that we have a genuinely protected space throughout Gaza, a space in which the humanitarians can not only continue to do their work, but massively increase it to the benefit of people who desperately need it", he said.