The airdrops, which some aid experts criticized as insufficient and largely symbolic, contribute “to ongoing U.S. government efforts to provide lifesaving humanitarian assistance to the people in Gaza,” the statement said. “We are conducting planning for potential follow-on airborne aid delivery missions.”

One of the U.S. officials briefing reporters on the operation on Saturday said that 66 pallets had been dropped over Gaza. The official said that drop sites had been chosen in relatively safe areas where people are sheltering and in need. The U.S. did not coordinate its operation with Hamas or any other group on the ground, the official said.

The operation was intended to be the first in a sustained campaign of airdrops, the official said, adding that the United States is also exploring other avenues of bringing more aid into Gaza, including by sea. The official and others at the briefing spoke on the condition of anonymity to discuss military operations and diplomatic efforts.

The drops came a day after President Biden said the United States would find new ways to get aid to Palestinians in desperate need because of Israel’s five-month military campaign to destroy Hamas. It also comes two days after more than 100 Palestinians were killed as Israeli forces opened fire around a convoy of aid trucks in northern Gaza.

Although Mr. Biden has implored Israel, which has sealed its border with Gaza, to allow more aid in, the demand for food, water and medicine after nearly five months of war there remains huge. Those conditions have put Mr. Biden under political pressure to do more to help the Palestinians even as the U.S. supplies Israel with military hardware.

Despite his frustrations with Israel’s political leadership, Mr. Biden has declined to threaten any limits on American aid to the country as a way of shaping its military offensive.

The convoy disaster on Thursday underscored the desperation Palestinians in Gaza face, and the fact that the ground convoys Israel has allowed into the territory have not provided enough relief.

U.S. officials have cautioned that airdrops cannot move supplies at the scale of convoys. Even big military cargo planes, like the C-130 airplanes used on Saturday, can carry only a fraction of the supplies that a convoy of trucks can haul. In addition, aid dropped on the ground is difficult to secure and distribute in an orderly way.

The United States’ top goal, the officials said in Saturday’s briefing, is to negotiate a pause in fighting that would allow far more truck traffic to enter.

The Biden administration is still working to achieve a limited cease-fire along with an increase in aid into the enclave and the release of “vulnerable” Israeli hostages in Gaza in return for Palestinian prisoners in Israel.

Israel has agreed to a plan that would include a six-week cease-fire, another U.S. official said Saturday. The official added that the United States and other countries, including Egypt and Qatar, are trying to persuade Hamas to accept the deal.

It was not clear when the next airdrop might be, as poor weather was forecast for Gaza on Sunday.

As hunger and illness grow in Gaza, U.S. officials have pressured Israel to allow more aid convoys into the territory, with limited success.

A third U.S. official briefing reporters on Saturday said that the shortage of supplies has been compounded by lawlessness within Gaza, which has made effective distribution difficult. Criminal gangs are plundering aid and selling it for exorbitant prices. Flooding Gaza with supplies will lower prices and reduce the incentive for theft, the official said.

Some humanitarian aid experts were critical of the U.S. airdrops as far too little to make a real difference. Dave Harden, a former Gaza director at the U.S. Agency for International Development, wrote on social media that “there will be no meaningful humanitarian impact in Gaza” from the drops.

Without security in the drop zone and coordination with relief workers on the ground, he said, “assume that the strongest — not the most vulnerable and needy — will take and control the food.”

On Friday, the International Rescue Committee said airdrops “do not and cannot substitute for humanitarian access.” The group urged Israel to reopen border crossings in northern Gaza and let aid flow in. Airdrops “distract time and effort from proven solutions to help at scale,” the committee said, adding that more than half million people in Gaza “are facing famine conditions.”

Eric Schmitt contributed reporting.