The UN on Monday said Israeli authorities blocked more than half of the 115 planned humanitarian aid deliveries to northern Gaza in June.
Speaking at a news conference, spokesman to the secretary general, Stephane Dujarric, said there are "little or no" available shelters or critical supplies in the areas where people have been forcibly displaced.
Aid distribution through the Kerem Shalom crossing was "nearly impossible" due to security and fuel shortages, he added.
Israel has killed nearly 38,000 Palestinians since an Oct. 7, 2023 cross-border attack by Hamas. Israeli actions have triggered a humanitarian disaster and an ongoing trial over alleged genocide at the International Court of Justice.
Dujarric conveyed the warning by humanitarian workers, saying: "The unexploded ordinance continues to pose a significant risk to the lives of people all across Gaza, that includes internally displaced people and people trying to return to areas from once they came, children are particularly at risk."
He said a 9-year-old girl was killed by unexploded ordnance in Khan Yunis on Saturday.
"It just shows yet again, that no place is safe in Gaza, that more efforts need to be made to protect civilians," he added.
Dujarric said the UN World Food Program (WFP) had transferred some aid from the floating pier U.S. built in Gaza, adding: "We still don't have the green light from our security colleagues to operate to take material from the pier."
Noting that the floating pier currently is not operating, Dujarric said the WFP had contracted a private company to transport the aid from the pier to prevent it from spoiling and going to waste.
