(Reuters) - The United States on Saturday carried out the first of what it said would be a series of humanitarian airdrops of food into Gaza, as aid agencies warned of a growing humanitarian disaster in the Palestinian enclave in the absence of a ceasefire deal.

Three C-130 U.S. military planes delivered more than 38,000 meals into a territory where the United Nations says at least 576,000 people are one step away from famine conditions. Palestinians posted videos on social media showing boxes of aid being dropped. Jordanian forces also participated in the operation.

The White House has said the airdrops would be a sustained effort, and that Israel supports them.

Critics say airdrops are far less effective than aid deliveries by truck, and it is nearly impossible to ensure supplies do not end up with militants.

"Israel welcomes the humanitarian airdrops by the U.S., which were discussed and coordinated with us," said an Israeli official in Washington, speaking on condition of anonymity.

With talks in Egypt to resume on Sunday, a senior U.S. official said the framework for a deal on a six-week ceasefire was in place, with Israel's agreement, and depended on the militant group Hamas agreeing to release hostages.

"The hostages have to be released," the official told reporters. "The deal is basically there. But I don't want to create expectations one way or the other."

U.S. Vice President Kamala Harris will meet Israeli war cabinet member Benny Gantz at the White House on Monday, a White House official told Reuters.

In Jerusalem, thousands of Israelis marched to demand the release of about 134 hostages held by Hamas in Gaza. Protesters, led by families of hostages seized during Hamas' deadly rampage through southern Israel on Oct. 7, arrived at the city at sundown.