UNITED NATIONS (Reuters) - A backlog of 1,150 truckloads of humanitarian aid is waiting to be collected from the Palestinian side of the Kerem Shalom crossing in the southern Gaza Strip, Israel said on Wednesday, prompting the United Nations to say: "We're doing what we can."

COGAT, an Israeli defence ministry agency tasked with coordinating aid deliveries into Palestinian territories, said another 50 aid trucks are also awaiting collecting from the Palestinian side of the Erez crossing in northern Gaza.

The United Nations said it is struggling to distribute aid within the enclave of 2.3 million people as the war between Israel and Palestinian militants Hamas enters its tenth month and law and order has broken down.

"Yes the aid is being dropped off. But on the other side of that you have utter lawlessness, plus you have continuing conflict," said U.N. spokesperson Stephane Dujarric. "We are continuing to do our best to get that to those people who need it. Our colleagues in Gaza are not sitting on their hands."

He said that the U.N. trucks that manage to pick up aid "are doing it often at great cost, because they are being either looted or attacked by criminal elements," adding that: "Some aid is getting through, but very little."

The United Nations has long complained of dangers and obstacles to getting aid into Gaza - Israel inspects and approves all aid trucks - and distributing it within the enclave, where a global hunger monitor last month said there is a high risk of famine.

The top U.N. aid official for the Occupied Palestinian Territory, Muhannad Hadi, briefed U.N. Secretary-General Antonio Guterres on Wednesday - a day after visiting Gaza - Dujarric said. Hadi entered and exited through the Kerem Shalom crossing.

"He saw groups of men with sticks waiting for trucks to leave the Kerem Shalom crossing into Gaza. All the trucks that he passed were badly damaged, with broken windshields, mirrors and hoods," Dujarric told reporters.

Hadi also saw bags of fortified flour from the World Food Programme (WFP) and the U.N. Palestinian refugee agency UNRWA scattered alongside the road from Kerem Shalom into Gaza, Dujarric said.

In northern Gaza, WFP said military activity was limiting its operations. Israeli forces continued to press their offensive in north and central Gaza on Wednesday, dropping leaflets urging the evacuation of Gaza City.

WFP has not delivered any food from the West Erez crossing for a couple of days, said WFP spokesperson Shaza Moghraby.

"Distribution sites have been evacuated and shut down, terrified people are being displaced again and every time this happens it makes it more difficult for us to reach them so there is a major impact on our operations," she said.

(Reporting by Michelle Nichols; Editing by Josie Kao)

By Michelle Nichols