Trucks of humanitarian aid began moving ashore into Gaza early Friday via a temporary pier built by the U.S. military, the first supplies of aid to be sent into the enclave by sea in two months. But the new shipments of food and other supplies fall far short of what humanitarian groups say is needed to meet the staggering levels of hunger and deprivation in Gaza.

A day earlier, the U.S. military said it had anchored the floating pier and causeway to the beach in Gaza, a key step in completing a maritime corridor that the Pentagon announced in March. U.S. officials and international aid groups have said that sea shipments can only supplement deliveries through land crossings, not replace them.

No U.S. troops entered Gaza on Friday, the U.S. military said, emphasizing that it was providing only logistical support for delivery of the supplies, which were donated by a number of countries and organizations.

The war-torn territory of 2.2 million civilians is more reliant than ever on humanitarian aid. The devastation after seven months of Israeli bombardment, strict Israeli inspections and restrictions on crossing points had already severely limited what could enter. And over the past week and a half, since Israel began a military assault around the city of Rafah, the flow of supplies through the main land crossings in southern Gaza had been reduced to a trickle.

Aid agencies continued to report increasingly dire conditions in Gaza. Janti Soeripto, president and chief executive of Save the Children U.S., told The New York Times on Friday, “We have never ever seen anything like this anywhere in the planet.”

Israel has come under pressure from the Biden administration and other allies to do more to ease the entry of aid, with Secretary of State Antony J. Blinken warning this week that recent improvements in relief delivery were being undercut by fighting in and around Rafah.

More than 630,000 Gazans have fled Rafah since Israel began its military offensive there on May 6, according to the main U.N. agency that aids Palestinians. Many have been displaced to the central city of Deir al Balah, which the U.N. agency, known as UNRWA, said on social media was now “unbearably overcrowded with dire conditions.”

This week, top diplomats of 13 countries — including every member of the Group of 7 industrialized democracies except the United States — said in a joint letter, a copy of which was seen by The New York Times, that Israel must take “urgent action” to address the humanitarian crisis in Gaza. The letter, addressed to Israel’s foreign minister, calls on the Israeli authorities to expand the amount of aid entering the territory, take “concrete action” to protect civilians and work toward a “sustainable cease-fire.”

On Friday, at a hearing at the International Court of Justice in The Hague, lawyers representing Israel defended the military operation in Rafah as “limited and localized,” arguing that the judges should not seek to restrict Israel’s actions in Gaza.

The hearings at the court, the U.N.’s highest judicial body, are part of a case filed by South Africa in December that accuses Israel of committing genocide against Palestinians in Gaza. In late January, the court ordered Israel to do more to prevent acts of genocide, but it is not expected to hear the main case over whether genocide is being committed until next year.

Last week, South Africa asked the judges to issue an emergency order aiming to prevent wide-scale civilian harm in Rafah. Lawyers for South Africa argued at the court on Thursday that Israel’s Rafah operation was “the last step in the destruction of Gaza and its Palestinian people.”

On Friday, Gilad Noam, the Israeli deputy attorney general for international law, repeated Israel’s fierce rejection that it was committing genocide in Gaza. He said the Israeli authorities were working to facilitate the flow of humanitarian aid and to protect civilians amid fierce combat across the enclave, including in Rafah.

“Israel is taking steps to try and contend with the massive complexity that such a situation presents,” Mr. Noam told the judges. “That is why there has not been a large-scale assault on Rafah, but rather specific, limited and localized operations prefaced with evacuation efforts and support for humanitarian activities.”

Israel’s military has said it is working with the U.S. military to support the temporary pier project as a “top priority.”

The supplies that began arriving Friday were a fraction of the need in Gaza: food bars for 11,000 people, therapeutic food for 7,200 malnourished children and hygiene kits for 30,000 people, according to the U.S. Agency for International Development. The British government said it had sent 8,400 temporary shelters made up of plastic sheeting.

“More aid will follow in the coming weeks, but we know the maritime route is not the only answer,” Prime Minister Rishi Sunak of Britain said in a statement.

It was not immediately clear where in the enclave the aid would be delivered or when. The U.N. World Food Program said in a statement that it would handle logistics in Gaza for aid coming through the pier, including coordinating trucks, overseeing the loading of supplies, dispatching them to warehouses and handing them over to “humanitarian partners.”

Pentagon officials said they were initially aiming to deliver about 90 trucks of aid by sea each day, increasing that to about 150 trucks when the operation reached capacity. Some 500 trucks of commercial goods and aid arrived in Gaza each day before the war began last October.

Defense Secretary Lloyd J. Austin III spoke about the maritime corridor in a call with his Israeli counterpart, Yoav Gallant, on Thursday, according to the Pentagon. Mr. Austin stressed the need to “surge” humanitarian assistance to Gaza through land border crossings in addition to the pier, according to the department.

Vice Adm. Brad Cooper, deputy commander of the Central Command, said the pier would only complement the flow of aid through land crossings, which he emphasized were “the most efficient and effective pathway to move the necessary volume of assistance.”

One of Gaza’s two main crossings for aid, in Rafah on the border with Egypt, has been closed since Israel began its military operation against Hamas fighters there. Israel shut down the second major crossing, at Kerem Shalom, after a Hamas rocket attack nearby killed four Israeli soldiers last week. That crossing has since reopened, Israel says.

An aid group, World Central Kitchen, built a makeshift jetty in mid-March to deliver aid by sea to Gaza for the first time in nearly two decades. But those efforts came to an abrupt stop in early April after seven of the group’s workers were killed in an Israeli strike.