Humanitarian assistance -- and particularly food - is desperately needed across Gaza, particularly in northern areas, Mr. Casey said.

"The food situation in the north is absolutely horrific, there's almost no food available," he told journalists in Geneva via video. "Everybody we talk to begs for food and comes up and asks, 'Where, where's the food?' People help us get our medical supplies through. But they are constantly telling us that we need to come back with food."

Echoing that appeal and expressing concerns about intensifying hostilities in the south, Dr Rik Peeperkorn, WHO Representative for the Occupied Palestinian Territory, explained that moving staff and supplies "safely and swiftly" had been compromised, "as deconfliction is required for any moves across Gaza, including the south - often leading to delays".