A U.S. drone strike on Sunday destroyed an explosives-laden vehicle that the Pentagon said posed an imminent threat to Afghanistan’s main airport, as the massive airlift of Afghans fleeing Taliban rule shut down just two days before the scheduled final withdrawal of American forces.

Afghans said the drone strike killed as many as nine civilians, including children, and the U.S. military said it was investigating the assertions.

The U.S.-led coalition told Afghans awaiting transport out of the country that for them the airlift was over. “We regret to inform you that international military evacuations from Kabul airport have ended,” it said in a text message sent late Saturday night, “and we are no longer able to call anyone forward for evacuation flights.”

The airlift has flown more than 117,000 people out of the country since Aug. 14, most of them Afghans, and some Afghans may already be in the airport waiting for flights, but it is leaving untold thousands behind. The desperate, dangerous scramble to reach Kabul’s international airport and the deadly attack there last Thursday by an Islamic State branch have defined the chaotic and bloody end to America’s longest war.

The U.S. military rushed to fly its remaining service members and equipment from the airport, its last outpost in Afghanistan, ahead of the Tuesday deadline set by President Biden to close out a war that began after the Sept. 11 attacks in 2001. Britain, which has played the second-largest role among NATO forces in Afghanistan, withdrew its last troops on Sunday.

For Americans and their allies, the final days in Afghanistan continue to be among the most perilous and uncertain. For several days U.S. officials have cited “specific, credible threats” of impending attacks, and the Pentagon has stopped publicly stating the declining number of troops at the airport for security reasons.

Afghans have lived for nearly 20 years under an American security umbrella that held out the promise of a better future and allowed for a more modern society connected to the rest of the world. With the return of the Taliban, that dream has died and an uncertain future beckons, especially for women and girls, who were brutally oppressed under the Taliban a generation ago.

The Islamic State branch known as ISIS-K carried out the airport bombing last week which killed an estimated 180 people, including 13 U.S. service members, and American officials have warned repeatedly that more attacks are expected. Two Britons and the child of a Briton were also among those killed in the suicide bombing.

The U.S. military carried out a retaliatory drone strike on Friday that officials said killed two ISIS-K members. The Pentagon said the strike on Sunday in Kabul destroyed a vehicle and killed one to three occupants wearing suicide-bombing vests. The drones operated from a base in the United Arab Emirates, more than 1,000 miles away — a glimpse of how future American warfare may be conducted.

“We are confident we successfully hit the target,” a spokesman for U.S. Central Command, Capt. Bill Urban, said in a statement describing Sunday’s strike. “Significant secondary explosions from the vehicle indicated the presence of a substantial amount of explosive material.”

The chief Taliban spokesman and people in Kabul who posted on social media said that both a house and a vehicle had been hit in a neighborhood just west of the airport and that several civilians had been killed, as well.

Samim Shahyad, a 25-year-old journalism student, said the strike killed his father, his two brothers, four of his young cousins, his niece and his sister’s fiancé. Three of the dead were girls 2 years old or younger, he said, and his aunt and uncle lost all three of their children.

“The American aircraft targeted us,” he said. “I do not know what to say, they just cut my arms and broke my back, I cannot say anything more.”

A doctor at a nearby hospital said four bodies were taken there, two of them those of children.

A senior U.S. military official responded that the military was confident that no civilians had been in the targeted vehicle but acknowledged that the detonation of the explosives in it could have caused “collateral damage.”

Video of the scene showed a tangle of metal barely recognizable as the remains of a vehicle, and just a few feet away, the charred, pockmarked wreck of another vehicle, an S.U.V. Mr. Shahyad said his father had been pulling into their garage when the explosion hit.

Mr. Biden traveled on Sunday to his home state, Delaware, to join the families of the 13 service members who were killed on Thursday by a suicide bomber as they screened people entering the airport for the evacuation effort.

The president and first lady, Jill Biden, met with the families on Sunday morning, then stood somberly with Defense Secretary Lloyd J. Austin III and other officials as the flag-draped coffins were carried from a military transport plane.

Over nearly two decades, the war has claimed the lives of more than 2,400 U.S. troops, more than 1,100 service members from allied nations, more than 3,800 American contractors, more than 500 aid workers and journalists, more than 47,000 Afghan civilians, as many as 69,000 Afghan soldiers and police officers and about 51,000 insurgent fighters, according to Brown University’s Costs of War project.

Tens of thousands of Afghans with connections to NATO military and diplomatic efforts or the toppled, U.S.-backed Afghan government continue to seek ways out of the country for fear of Taliban reprisals. Thousands of those who thronged to the airport in the last two weeks — risking ISIS-K attacks, trampling by those around them and beatings by Taliban fighters trying to control the crowd — were unable to get past the gates.

The U.S. government is aiding about 250 American citizens still in Afghanistan who are trying to leave, some of whom were already at the airport, and is aware of about 280 others who have chosen not to leave for now, the State Department said on Sunday.

Despite Taliban vows of no reprisals against former adversaries, there have been reports that the militants have rounded up and killed Afghans who worked with the former government or its foreign backers.

The United States and 97 other countries said on Sunday that they had “received assurances from the Taliban” that Afghans with travel documents for those countries would be permitted to leave Afghanistan after U.S. troops depart.

The countries also pledged to “continue issuing travel documentation to designated Afghans” and cited a “clear expectation of and commitment from the Taliban” of their safe passage. Notably missing from the statement were Russia and China, two permanent members of the United Nations Security Council who have pledged to help the Taliban rebuild Afghanistan.

The Taliban’s chief negotiator, Sher Mohammed Abas Stanekzai, announced on Friday that the group would not stop people from departing, no matter their nationality or whether they had worked for the United States during the 20-year war.

But the Taliban have reneged on promises in the past, and their leaders have not always been able to control fighters and followers on the ground. Some aid groups, unwilling to trust assurances that they can get people out through the airport, are attempting arduous and dangerous overland journeys.

The rapid American exit has left much of Afghanistan awash in grief and desperation, with many people fearing for their lives under Taliban control and struggling to support their families amid cash shortages and rising food prices. Some banks opened in Kabul on Sunday, and long lines formed outside their doors.

International aid groups have warned that a continuing humanitarian crisis, compounded by war and drought in recent months, has only grown worse during the dislocation and upheaval set off by the rapid Taliban takeover and the U.S. withdrawal.

The signal achievements of the America era are now under threat: education and a role in public life for women; a vibrant, independent news media; elections for national leaders; and maintenance of new hospitals, roads and public services.

Secretary of State Antony J. Blinken said Sunday that it was “not likely” that the United States would keep diplomats in Afghanistan after the military departs on Tuesday, formally shuttering one of the largest American embassies in the world. The last British diplomats in Afghanistan left on Sunday and said they would operate for the time being from Qatar.

Western nations are unsure whether their people can operate safely in Afghanistan and are reluctant to recognize the Taliban fully as the Afghan government.

Officials said it was expected that the United States would open a diplomatic mission in another country in the region for dealing with the Taliban. Possibilities include Pakistan and the United Arab Emirates, where there are many Afghan expatriates, and Qatar, where there is a major U.S. military base and where the Taliban participated in talks with the United States and the former Afghan government.

After saying last week that the Biden administration was reviewing options for the future of the embassy in Kabul, Mr. Blinken told NBC’s “Meet the Press” on Sunday that “in terms of having an on-the-ground diplomatic presence on Sept. 1, that’s not likely to happen.”

“But what is going to happen is that our commitment to continue to help people leave Afghanistan who want to leave and who are not out by Sept. 1, that endures,” Mr. Blinken said. “There’s no deadline on that effort. And we have ways, we have mechanisms to help facilitate the ongoing departure of people from Afghanistan if they choose to leave.”

The Taliban had wanted the United States and other foreign governments to remain in Kabul as a symbol that they recognize their legitimacy.

Prime Minister Boris Johnson of Britain, praising his nation’s evacuation efforts in an address posted to Twitter, said that troops and officials had worked around the clock “to a remorseless deadline in harrowing conditions” to airlift more than 15,000 people, including Britons and Afghans, to safety in less than two weeks.

One symbol of the freedoms young Afghans have enjoyed in recent years was mingling in Western-style coffee shops, which have blossomed in Kabul. The shops have been among the few public places where unmarried young men and women can mingle and flirt.

But on Sunday, there were few customers — and just two women, both conservatively dressed — in one coffee shop in Kabul, where two young men huddled to commiserate about their fates and that of their country. Both men said they had applied for the special immigrant visas granted to Afghans who worked for the U.S. military or government agencies but had been unable to reach the airport to get aboard an evacuation flight.

One man wore a T-shirt and jeans, Western attire favored by many young men in Kabul but viewed with suspicion by some Taliban members. Both men had begun growing beards to blend in on streets patrolled by Taliban gunmen. The group required men to grow beards when they controlled most of the country from 1996 to 2001.

Outside, amid the bustle of open markets along the sewage-clogged Kabul River, families desperately sought to buy fruit and vegetables or secondhand household items left behind by fleeing families.

“From the outside, it may look like we’re calm and everything’s fine,” one of the men in the coffee shop said. “But inside, the tension is too much.”

Reporting was contributed by Helene Cooper, Eric Schmitt, Lara Jakes, Jim Tankersley, Thomas Gibbons-Neff, Najim Rahim, Fatima Faizi, Fahim Abed, Jim Huylebroek, Dan Bilefsky and Isabella Kwai.