But so far, the movement lacks the clear support of two countries that supply almost all imported weapons to Israel: the United States and Germany. Both voted against the nonbinding resolution at the U.N. Human Rights Council this week.

The United States and Germany supply roughly 99 percent of all arms imported to Israel, according to an analysis published in March by the Stockholm International Peace Research Institute (SIPRI).

By SIPRI’s estimates, Israel imported 69 percent of its arms from the United States and 30 percent from Germany from 2019 to 2023. That’s partly a reflection of where arms manufacturers are located but also a result of government policy. U.S. aid to Israel comes largely in the form of grants for use on U.S.-made military equipment. The German government, meanwhile, has made export approval of German-made arms for Israel a priority.

Both President Biden and German Chancellor Olaf Scholz expedited arms shipments for Israel after the Oct. 7 attacks on the country that left 1,200 dead.

“The United States is the key to arms restrictions having any significant impact on Israeli policy,” said Seth Binder, an expert at the Middle East Democracy Center.

There are signs that leverage can work. During a phone call with Israeli Prime Minister Benjamin Netanyahu on Thursday, Biden told the Israeli leader that there needed to be “specific, concrete, and measurable steps to address civilian harm, humanitarian suffering, and the safety of aid workers,” the White House said in a statement.

Only hours later, Israel’s war cabinet announced new measures to allow more aid into Gaza, including the opening of the Erez border crossing, a move humanitarian groups had requested for months. Sen. Chris Van Hollen (D-Md.) said he hoped that was a sign that the Biden administration had indicated it was serious about potentially curtailing support for Israel.

“The goal is not to stop all arms transfers. The goal is to use the leverage of arms transfers to enforce our legitimate demands,” Van Hollen said in an interview.

“We went through a period where the Netanyahu government ignored the demands of the United States, and we sent 2,000-pound bombs” to Israel, he added. “I hope we’re now at a point where we are not providing a blank check.”

Others say the United States should go beyond threats. In a letter released Thursday, the Elders, a group of 12 global rights leaders chaired by former U.N. high commissioner for human rights Mary Robinson, said the United States should spearhead an arms embargo.

“As Israel’s closest ally and its largest provider of arms, the United States of America must lead the way,” the group’s statement said.

More than 160 humanitarian organizations and rights groups have signed on to a call for an arms embargo, first issued Jan. 24. New signatories joined after Israeli airstrikes killed seven members of a World Central Kitchen aid convoy Monday, highlighting the dangers of humanitarian operations in Gaza.

National and regional governments in Belgium, Canada, Italy, the Netherlands and Spain have suspended arms sales to Israel, citing concerns about international humanitarian law. The Japanese firm Itochu announced in February that it would end its partnership with a major Israeli defense contractor in response to a ruling by the International Court of Justice.

In Denmark, human rights groups last month sued the government to block the export of weapons and other military equipment to Israel, while French lawmakers wrote to President Emmanuel Macron on Friday to demand a similar move.

Among the strongest reactions has been in Britain, a key ally of both Israel and the United States. There, the deaths of three British citizens in the strike on the World Central Kitchen workers have stoked public outrage. More than 800 legal experts wrote to the government this week to say that the country needed to halt arms exports to Israel to avoid “complicity in grave breaches of international law.”

“Enough,” read Thursday’s front page of the Independent, which said it was time “to do whatever it takes” to stop the war.

Friday’s resolution at the 47-member U.N. Human Rights Council passed by a vote of 28 to 6, with 13 abstentions. As a nonbinding resolution, however, it is unlikely to have practical impact on arms sales to Israel.

The United Nations can impose mandatory arms embargoes on nations through a Security Council vote, as it did on apartheid-era South Africa. However, the United States holds veto power. “As a result, there is almost no chance of a U.N. arms embargo against Israel,” said Jennifer L. Erickson, an arms-control scholar at Boston College.

Erickson added that the European Union could implement a bloc-wide arms embargo, as it has done in other cases. “But this would still in practice require the consensus of all the E.U. member states,” Erickson said — meaning Germany would have to agree.

The United States has been the most significant supporter of Israel’s military by far, providing billions of dollars of aid annually. Most of it falls under the Foreign Military Financing program, which provides grants to purchase U.S. military goods and services.

German arms exports to Israel surged tenfold last year compared with 2022, hitting $354 million. Of that, roughly $22 million was offensive weapons, including 3,000 portable antitank weapons and 500,000 rounds of ammunition for machine guns, submachine guns, or other fully automatic or semiautomatic firearms. Most exports were approved after Oct. 7.

The German government’s unflinching support is based on the notion that Israel’s security and right to exist are part of Germany’s historical responsibility and “reason of state,” a formulation first used by Angela Merkel in 2008.

“I think with that declaration in 2008, Germany really put itself into a straitjacket and sort of voluntarily gave away its options,” said Daniel Marwecki, author of “Germany and Israel: Whitewashing and Statebuilding.”

Unlike the United States, Germany is a party to the U.N. Arms Trade Treaty, which could prohibit the sale of certain arms to Israel if there was a risk they could be used to break international humanitarian law. Domestic law could provide an additional constraint. On Friday, human rights lawyers in Germany filed an urgent court appeal, demanding that the government cease authorization of war weapons for Israel, in accordance with the country’s War Weapons Control Act.

Amanda Klasing, director of advocacy at Amnesty International USA, said her organization is trying to make the case to the U.S. government that its arms shipments to Israel are violating international obligations. “There is enough evidence to leverage existing law and policy to suspend arms transfers,” she said. “Ultimately, it is a political choice to keep sending arms.”

The United States has supplied Israel with numerous shipments of heavy weaponry that has been used in Gaza since Oct. 7, including heavy bombs and Joint Direct Attack Munition systems that can be fitted to turn them into guided weapons.

“The United States used an emergency provision to rush 155mm artillery ammunition to Israel in December,” said Binder of the Middle East Democracy Center. “If Israel did not receive a resupply of these shells, it could not have conducted operations in the same way.”

The State Department authorized the transfer of 25 F-35A fighter jets and engines last month. A judge in the Netherlands recently ruled that there was “a clear risk that serious violations of humanitarian law of war” would be committed by F-35s used by Israel and blocked the export of parts for the jets.

White House national security adviser John Kirby told reporters this week that the State Department was continuing to review Israeli actions in Gaza but that officials “haven’t found an incident yet that has pointed to a violation of international humanitarian law.”

The State Department and the Department of Defense both have mechanisms for assessing whether U.S. arms are being used to breach law, the former of which was put in place by the Biden administration last year.

In February, Biden issued a national security memorandum that expanded upon those rules, adding an annual report to Congress about whether recipients of U.S. arms are meeting the standards. Nonprofit organizations that track the use of U.S. arms in Israel have said the process has been burdensome and unclear.

Ellen Francis contributed to this report.