Israeli troops have opened fire on U.N. aid convoys to northern Gaza at least four times in three months, according to U.N. and other humanitarian officials, damaging the vehicles and narrowly missing staff members inside. On Sept. 9, the officials said, the Israeli army held a convoy involved in the United Nations’ polio response at gunpoint for 7½ hours, claiming that several people in the vehicles were wanted men. They were questioned and eventually allowed to proceed.

“They basically surrounded our vehicles, pointing assault rifles at our cars, and they were shouting that we’re terrorists,” said one U.N. staffer who, like others interviewed for this article, spoke on the condition of anonymity because of the sensitivity of the issue.

U.N. officials describe the Sept. 9 incident as emblematic of an environment of mistrust, in which Israeli soldiers, many of them reservists, command significant power at the checkpoints that humanitarian workers must cross to enter northern Gaza and face few consequences for their actions.

The Biden administration intensified pressure on Israel this week to improve the dire humanitarian conditions in the Gaza Strip, as officials in Washington warned of punitive measures, potentially including a suspension of military aid, if aid flows are not increased within a month.

The Israeli army said in a statement to The Washington Post about the convoys that it makes “significant efforts” to facilitate the passage of aid through Gaza and that all units include civil affairs officers “specifically trained to cope with and manage issues related to the civilian population at the command, division, brigade and battalion levels.”

The Post provided the Israeli military with a detailed list of incidents in which troops are alleged to have opened fire, but it received no further response.

“Our colleagues risk their lives to save others and too often come under fire. Throughout this conflict, we have demanded respect for international humanitarian and human rights law. There must be accountability,” said Jonathan Whittall, acting head of the U.N. Office for the Coordination of Humanitarian Affairs in the Palestinian territories. “In no other context would we accept to operate in such conditions, but in Gaza, people cannot leave the war zone and seek assistance elsewhere.”

A year into Israel’s military operations in Gaza, the besieged enclave has become the most dangerous place in the world for relief workers, according to aid groups. The United Nations says that more than 280 staffers have been killed in Israeli attacks on aid depots and convoys and on residential homes. Some humanitarian workers have been killed or wounded with U.S. weapons, aid groups say.

Israel and the United Nations have long been at loggerheads, but the tensions have soared in the year since the devastating cross-border Hamas-led attack on southern Israel, which killed about 1,200 people and sparked the war in Gaza.

Israeli officials have alleged that the U.N. agency for Palestinian refugees, or UNRWA, is an instrument of Hamas, claiming at different times that dozens or thousands of employees are associated with the militant group. The agency said in August that it had fired nine employees after an investigation into the Israeli claims but said that a broader Israeli disinformation campaign to defame UNWRA, which employs 13,000 people in Gaza, was endangering its staff.

Israel’s foreign minister said this month that he was barring U.N. Secretary General António Guterres from entering the country because he had not “unequivocally” condemned an Iranian missile attack on Israel amid an escalation in fighting between Israel and Hezbollah, an Iranian proxy in Lebanon. U.N. spokesperson Stéphane Dujarric described the announcement as “one more attack on the United Nations staff that we’ve seen from the government of Israel.”

One of the few times the Biden administration clashed openly with Israel came after its forces killed seven employees of the nonprofit World Central Kitchen, six of whom were foreign nationals, as they traveled along an agreed-upon route in central Gaza.

Although most of the aid workers killed during this conflict have been Palestinian, the deaths of foreign staffers has drawn the most international scrutiny. U.S. officials said President Joe Biden was “shaken” by the strike on the World Central Kitchen, whose president, José Andrés, he calls a “friend.”

“This week’s horrific attack on the World Central Kitchen was not the first such incident. It must be the last,” Secretary of State Antony Blinken told reporters days later, adding that Biden had told Israeli Prime Minister Benjamin Netanyahu that U.S. policy would be “determined by our assessment of Israel’s immediate action” with regard to limiting civilian harm and attacks on aid workers.

But the humanitarian crisis has only worsened, and aid groups say they have witnessed no significant efforts to improve the flow of supplies or better protect the staffers delivering them. Last month, UNRWA said six team members were killed in an Israeli airstrike as they assisted displaced civilians in a shelter.

For convoys transporting aid and personnel around Gaza, Israeli checkpoints to the north — the entry point to the part of Gaza where troops have fought fierce battles with Hamas militants — have become among the most dangerous flash points.

To pass, U.N. and other international aid groups submit their staffing lists to a branch of Israel’s Defense Ministry, the Coordinator of Government Activities in the Territories, or COGAT, for approval. Once it is granted, a convoy leaves the staff guesthouse after receiving an Israeli green light the following morning. Near the checkpoint, it again waits for a green light to move from a holding area to the checkpoint itself, where the identities of Palestinian and international staffers are checked, before the vehicles can pass through into northern Gaza.

When problems arise on the ground, humanitarian personnel often find that the COGAT interlocutors with whom they are in touch are unaware of the situation in real time, according to seven aid workers interviewed for this article. At times, humanitarian staffers have found themselves explaining to soldiers at checkpoints that they have received the official green light to move. “You say you’ve got it, but then they say: ‘No one told me, so you can’t pass,’ ” said one aid worker with an international group.

“When it works, it works really well. And when it doesn’t work, it really doesn’t work,” one senior U.N. staffer said.

On July 21, Israeli forces fired at a convoy with vehicles from UNRWA and other U.N. agencies as it awaited permission to move from a holding area at Wadi Gaza in central Gaza toward the checkpoint, the United Nations said. One vehicle was hit by five bullets. On July 23, two marked UNICEF vehicles were hit with three bullets at the same location. “They were en route to reunite five children, including a baby, with their father,” Adele Khodr, the agency’s regional director for the Middle East, said in a post to X.

On Aug. 27, Dujarric said, a vehicle carrying World Food Program staff was struck by Israeli gunfire 10 times near the Wadi Gaza checkpoint, with some shots targeting front windows.

The attack caused the agency to temporarily suspend staff movements inside Gaza. “The fact that it has been made more difficult for us to operate, it has been made more dangerous — they are targeting humanitarians — makes it doubly difficult for us to work,” said Cindy McCain, WFP’s executive director. “We are continuing to do the very best we can to get our commodities in and feed people, but I’ll tell you, it’s hard.”

Asked whether she thought that her staff were safe in Gaza, after the resumption of WFP missions there, McCain said: “Not really. There have been a lot of close calls.”

At the al-Rasheed checkpoint on Sept. 9, the situation escalated quickly, as soldiers pointed their weapons toward U.N. staff and then fired, Dujarric told reporters.

“The convoy was then approached by IDF tanks and a bulldozer, which proceeded to ram the U.N. vehicles from the back and front, compacting the convoy with U.N. staff inside,” he said. “One bulldozer dropped debris on the first vehicle, while Israeli soldiers threatened staff, making it impossible for them to safely exit their vehicles.”

“The convoy remained at gunpoint, as senior U.N. officials engaged with Israeli authorities in an effort to de-escalate the situation.” People with knowledge of the incident said staff were particularly alarmed at the request to detain and interrogate Palestinian colleagues because Palestinian aid workers on U.N. convoys had been detained on multiple occasions. Some, according to the Palestinian Red Crescent, had been severely beaten before being released on foot, miles from where they were detained. On Feb. 25, the United Nations said, Israeli forces blocked a World Health Organization convoy evacuating a hospital in Khan Younis, stripped Red Crescent paramedics and detained three of them.

According to three U.N. officials and a Western diplomat who was briefed on the Sept. 9 incident, Israeli soldiers at the checkpoint initially refused to stand down, despite an order from the Southern Command, which is responsible for all troops in Gaza. The standoff ended only after a senior Israeli commander arrived.

The Israeli army said in a statement that the convoy had been stopped on the basis of “intelligence.” It did not respond to questions about the troops’ conduct or how the incident ended.

U.N. officials say they have asked Israeli interlocutors on multiple occasions for better channels of communication on the ground, in the hope that it will reduce violent incidents. COGAT referred all questions about efforts to improve communications to the IDF.

The IDF said it had taken steps to strengthen coordination between the army and international aid groups, by distributing satellite phones to aid convoys, supporting efforts to attach visible identification symbols to the vehicles - something aid groups say they already have - and setting up a joint operations room to handle communications inside Gaza.