By Michelle Nichols

UNITED NATIONS (Reuters) - The United Nations Office for the Coordination of Humanitarian Affairs (OCHA) said 915 aid trucks entered the Gaza Strip on Monday, the second day of a ceasefire between Israel and Palestinian militants Hamas after 15 months of war.

OCHA cited information from Israel and the ceasefire guarantors, the U.S., Qatar and Egypt. On Sunday, the U.N. said some 630 aid trucks entered the Palestinian enclave, with at least 300 of them going to the north, where experts have warned a famine looms.

The ceasefire deal requires 600 truckloads of aid to be allowed into Gaza every day of the initial six-week ceasefire, including 50 carrying fuel. Half of the 600 aid trucks would be delivered to Gaza's north.

Data from the U.N. Palestinian relief agency UNRWA showed 2,892 aid trucks entered Gaza in December. Aid is dropped off on the Gaza side of the border, where it is picked up by the U.N. and distributed.

But gangs and looters have made that hard. Data from OCHA shows 2,230 aid truckloads - an average of 72 a day - were picked up in December, while between Jan. 1-5 it was a daily average of 51.

Israel has laid waste to much of Gaza and the pre-war population of 2.3 million people has been displaced multiple times. U.N. Secretary-General Antonio Guterres has described the humanitarian situation as "catastrophic."

Guterres told the U.N. Security Council on Monday that the U.N. still faces "significant obstacles, challenges and constraints." He said the U.N., aid groups and the private sector need rapid, safe and unimpeded access.

"Visas, permits, and other enabling conditions must be in place quickly to allow a surge of desperately needed relief," he told the 15-member council. "We require the necessary technical, protective and communications equipment."

Guterres said the parties - Israel and Hamas - must coordinate with the U.N. in a timely and effective manner so it can do its humanitarian work. "This also includes the restoration of public order and safety to prevent the looting of humanitarian supplies," he added.

He urged countries to take in people who need medical treatment, for sufficient commercial supplies to be able to enter Gaza and for explosive ordnances to be removed.

Israel says Hamas killed some 1,200 people in the Oct. 7, 2023 attack that triggered the war and the Gaza health ministry says more than 47,000 Palestinians have been killed in the conflict.

(Reporting by Michelle Nichols; Editing by Nia Williams)