UNITED NATIONS -- The Israelis allowed dozens of fuel trucks to cross into Gaza at Kerem Shalom on Tuesday but turned back trucks carrying other essential humanitarian cargo, UN humanitarians said.

"Humanitarian access into and out of Gaza for staff and goods must be sustained and appropriate measures taken to ensure safe movement within Gaza," the UN Office for the Coordination of Humanitarian Affairs (OCHA) said. "It is critical that the Erez crossing is also opened for the entry and exit of critical humanitarian staff."

Fuel is necessary to generate electrical power. The lack of it causes electrical blackouts lasting all but six to eight hours of a day. Additionally, electricity powers water pumps.

Stephane Dujarric, the chief spokesman for UN Secretary-General Antonio Guterres, told reporters in a regular briefing the only reason he knew for turning back some of the trucks was because of security.

Asked what was meant by the reason given, he responded that the Israelis only said "security."

Kerem Shalom is the only commercial crossing from Israel into Gaza.

The humanitarian office said it received reports about 58,000 Palestinians are displaced, with 47,000 of them seeking protection in 58 schools across Gaza run by the UN relief agency for Palestinian refugees known as UNRWA.

As far as the security situation allows, the United Nations and humanitarian partners provide food and non-food items to displaced families in Gaza and distribute immediate cash assistance to more than 56,000 people, OCHA said.

In the West Bank, widespread demonstrations and clashes continue, the humanitarians said. Health partners and community volunteers are treating a substantial number of people injured by Israeli forces gunfire.