One of the first aid shipments to arrive in the Gaza Strip through a U.S.-built pier was looted, officials said on Monday, highlighting the ongoing challenge of securely delivering humanitarian assistance in a territory with serious food shortages and other needs.

The failed delivery on Saturday came two days after the floating pier, constructed by the U.S. military at an estimated cost of more than $300 million, was connected to the Mediterranean shore in central Gaza. The U.S. State Department did not respond to requests for comment.

Crowds of Palestinians intercepted a convoy of trucks that had loaded goods from the pier, hastily grabbing and running off with its contents, according to Abeer Etefa, a World Food Program spokeswoman. Two senior Western officials and Majdi Fathi, a Gazan photo journalist, confirmed Ms. Etefa’s account. The officials requested anonymity because they weren’t authorized to speak publicly on the matter.

Aid groups and the United Nations blame the hunger crisis in Gaza on Israel’s restrictions on aid entering the enclave and also on black marketers who have seized supplies to sell at inflated prices. Israeli officials have insisted that enough supplies have been entering the territory and have accused Hamas of stealing and hoarding aid.

For months, as famine has threatened Gaza, Palestinians have forcibly taken aid off trucks. U.N. officials say the looting reflects the desperation of ordinary people trying feed themselves and their families, and they say it has decreased when large amounts of aid consistently enter the enclave.

On Saturday, 11 of 16 trucks that left the pier with aid were looted as they were on their way to a World Food Program warehouse, Ms. Etefa said, adding that the food aid agency had suspended deliveries from the pier on Sunday and Monday.

Footage taken by Mr. Fathi showed dozens of men chaotically grabbing and hurling boxes of supplies from the bed of a truck near Gaza’s coast. In an interview, Mr. Fathi, 43, a freelance photographer, said throngs of people had gathered on the coastal north-south road after hearing that a group of trucks had passed through the area the previous day.

“They completely emptied them,” he said.

In recent days, the aid has been driven from the pier to an Israeli-controlled section of Gaza. There, it has been offloaded from one set of trucks and put on another set of trucks before being transferred to population centers. It is unclear what arrangements have been made to guard the trucks after they leave the Israeli-controlled area

On Friday, 10 trucks carrying aid from the pier, including high-energy biscuits, had arrived at the W.F.P. warehouse without incident, Ms. Etefa said.

She said that incidents like the one on Saturday would recur as long as insufficient food assistance was reaching the people in Gaza, and that more Israeli-approved routes for delivering aid were needed to avoid crowds.

Aid delivery through the two main border crossings in southern Gaza increased sharply in April and early May, though it remained below the level that aid groups said was needed.

But since Israel invaded the eastern section of the southern city of Rafah on May 7 and closed the border crossing there, aid shipments through the southern routes has come to a near-halt, according to the primary U.N. agency for Palestinian aid. The agency, known as UNRWA, said that in a 15-day period through Monday, just 69 aid trucks entered through the two crossings — the lowest rate since the first weeks of the war.

In April, U.S. officials briefed reporters that they hoped the pier operation would initially bring in enough aid for around 90 trucks per day, before scaling up to 150 per day.

The war-torn territory of about 2.2 million civilians is more reliant than ever on humanitarian aid. The devastation after seven months of war and strict Israeli inspections and restrictions on crossing points has limited what can enter Gaza.

Eric Schmitt contributed reporting to this article.