UNITED NATIONS - UN Humanitarians said on Monday that access and security constraints hinder food aid delivery to hundreds of thousands of people in Gaza and the medical evacuation of 10,000 patients.

The UN Office for the Coordination of Humanitarian Affairs (OCHA) said the inability to transport aid commodities from the Kerem Shalom crossing safely and the continued closure of the Rafah crossing compounded the challenges facing aid operations.

OCHA said fewer than half of the 86 coordinated humanitarian missions to northern Gaza planned for this month were facilitated by Israeli authorities. More than a quarter were impeded, 12 percent were denied access and 12 percent were canceled due to logistical, operational or security reasons.

"A humanitarian mission returning to southern Gaza after delivering fuel and medical supplies to Gaza City in the north was delayed for more than 13 hours at an Israeli military checkpoint, putting the convoy in danger of being caught in crossfire," the office cited as just one example of the challenges in aid delivery. "Planned humanitarian missions requiring coordination to areas in southern Gaza also continue to face impediments and access denials."

The World Health Organization (WHO) reported that more than 10,000 people need medical evacuations to outside Gaza. WHO Director-General Dr. Tedros Adhanom Ghebreyesus appealed for their sustained medical evacuation and timely passage using all possible routes.

"Pediatric patients are among those who need to leave Gaza for specialized care," OCHA said. "WHO and partners transferred five of these patients -- four with cancer and one with second-degree burns -- from Al-Ahli hospital to Nasser Medical Complex, where they will continue to receive care until they can depart Gaza."

The humanitarians said the WHO team also delivered medical supplies to cover the health needs of 20,000 patients at Al-Ahli and As-Sahaba hospitals and 19,000 liters of fuel.

In short supply in Gaza, fuel is necessary for electricity generators and to power smaller vehicles transporting aid and personnel.