The first shipment of aid to reach Gaza by sea in almost two decades was fully unloaded on Saturday on a makeshift jetty in the Mediterranean, marking a milestone in a venture that Western officials hope will ease the enclave’s worsening food deprivation.

The ship, the Open Arms, towed a barge from Cyprus loaded with about 200 tons of rice, flour, lentils and canned tuna, beef and chicken, supplied by the World Central Kitchen charity.

José Andrés, the Spanish American chef who founded the World Central Kitchen, said his team would begin dispatching the food by truck, including to Gaza’s north, an area gripped by lawlessness and badly damaged by Israeli airstrikes.

But the distribution was set to unfold in the shadow of a series of attacks that have killed or wounded Palestinians scrambling for desperately needed food. United Nations aid groups had to largely suspend deliveries in northern Gaza last month, and its human rights office has documented more than two dozen such attacks.

The latest bloodshed took place late Thursday in Gaza City, where at least 20 people died after an aid convoy came under attack. Gazan health officials and the Israeli military traded blame; many details about what had unfolded remained unclear on Saturday.

World Central Kitchen offered few details about its distribution plan, even as it was loading a second supply ship in Cyprus. The Israeli military said in a statement that it had deployed naval and ground forces to secure the area where the supplies were unloaded, though it remained unclear who would handle the distribution.

“The Open Arms connected a barge filled with almost 200 tons of food to the W.C.K. built jetty on the coast of Gaza,” the charity said in a statement, referring to a jury-rigged pier it constructed out of rubble off the Gaza coast. “All cargo was offloaded and is being readied for distribution in Gaza.”

The 200 tons of food delivered by sea is the equivalent of about 10 truckloads, a drop in the bucket compared with the roughly 150 trucks a day that the United Nations relief agency, UNRWA, says are currently entering Gaza. And even that is only a fraction of what is needed, aid groups say, to provide adequate nutrition to Gazans.

With the enclave under a near-total blockade after more than five months of Israeli bombardment, the U.N. has warned that much of it is at risk of famine and called on Israel to ensure more food and medical care reach Gazans.

A new report released on Friday by UNICEF, the U.N. agency for children, found that children in the Gaza Strip were facing rapidly deepening food deprivation, and that an alarming number were suffering from “severe wasting,” the most life-threatening form of malnutrition.

Roughly one in every 20 children in shelters and health centers in northern Gaza has fallen into that condition, defined as being dangerously thin for their height, the report said. It cited screenings conducted by the agency.

The screenings found that acute malnutrition, meaning the body is deprived of essential nutrients, had become fairly common among children under 2 years old across Gaza. In some areas, rates of acute malnutrition had doubled since they were last recorded in January, the report said.

By comparison, the rate of acute malnutrition among young children was less than 1 percent before the war, UNICEF said.

The situation could soon grow more dire. Prime Minister Benjamin Netanyahu said on Friday that Israel was planning to move forward with a ground offensive in Rafah, a southern city where more than half Gaza’s population is sheltering.

Western officials were hopeful that negotiations over a cease-fire and a hostage and prisoner exchange would resume in the coming days. Mr. Netanyahu planned to dispatch an Israeli delegation soon to Qatar, the site of the mediation efforts.

Hamas has updated its own proposal, no longer demanding that Israel immediately agree to a permanent cease-fire and the withdrawal of Israeli troops from Gaza in return for beginning an exchange of hostages and prisoners, according to people familiar with the negotiations. Hamas dropped its demand for a permanent cease-fire and proposed the release of hostages in exchange for a phased pullback of Israeli troops from parts of the Gaza Strip as well as prisoner releases.

In the meantime, Israel remains under intense pressure to open more land crossings into Gaza to allow the acceleration of aid. Aid officials have emphasized that delivering supplies by sea or air is far less efficient than by truck.

The Open Arms is the first vessel authorized to deliver aid to Gaza since 2005, according to Ursula von der Leyen, the president of the European Union’s executive arm. She described the operation as a pilot project to study opening a maritime corridor to supply the territory.

The United States is also leading an initiative to put in place a temporary floating pier off Gaza’s coastline to ease the transit of goods. American officials hope the pier could make it possible to deliver two million meals a day for the area’s 2.3 million people.

World Central Kitchen is preparing to send a second ship with food from the Cypriot port of Larnaca, the charity said, but it was not clear when it would set sail. The vessel is equipped with two forklifts and a crane to assist with future maritime deliveries, and is expected to carry 240 tons of food, including carrots, canned tuna, chickpeas, corn, rice, flour, oil and salt, as well as over 250 pounds of fresh dates donated by the United Arab Emirates.

Since October, organizers and Palestinian cooks working with World Central Kitchen have served more than 37 million meals in Gaza, the group says.

The charity has also been sending aid by truck from its warehouses in Cairo and supplying food for airdrops conducted by Jordan and the United States. On Friday, 23 tons of food was dropped in the north, Mr. Andres said.

Monika Pronczuk reported from Brussels, and Gaya Gupta and Nicholas Fandos from New York. Raja Abdulrahim contributed reporting from Jerusalem.