The U.S. carries out a drone strike against an explosive-laden vehicle in Kabul.

A U.S. military drone strike blew up a vehicle laden with explosives in Kabul on Sunday, a Defense Department official said, hours after President Biden had warned that a terrorist attack against the Afghan capital’s airport was “highly likely.”

A spokesman for U.S. Central Command, Capt. Bill Urban, said the military was trying to determine whether the strike had caused civilian casualties, though he noted that there was no immediate evidence of that.

“U.S. military forces conducted a self-defense unmanned over-the-horizon airstrike today on a vehicle in Kabul, eliminating an imminent ISIS-K threat to Hamad Karzai International airport,” Captain Urban said, referring to the Islamic State Khorasan group. He added: “We are confident we successfully hit the target. Significant secondary explosions from the vehicle indicated the presence of a substantial amount of explosive material.”

Earlier Sunday, the United States Embassy in Kabul had said that there was a “specific, credible threat” to the airport area, where a suicide bombing on Thursday killed about 170 civilians and 13 members of the American military. State Department officials have issued several similar warnings in recent days.

With just two days left before Mr. Biden’s Tuesday deadline to complete the U.S. troop withdrawal from Afghanistan, the military was shifting its focus from vetting and airlifting Afghan and American civilians to bringing its own personnel home.

On Sunday morning, American University of Afghanistan students and their families boarded buses bound for the airport, on what could prove to be the last day of civilian evacuations. Some 300 American citizens still remain in Afghanistan, National Security Advisor Jake Sullivan said, in an interview on Fox News Sunday.

The American troop departures will mark the tumultuous end to a 20-year war that has left the country awash in grief and desperation, with many Afghans fearing for their lives under Taliban rule and struggling to support their families amid cash shortages and rising food prices. At least some banks had opened in Kabul on Sunday, and long lines had formed outside their doors.

The attack at the airport on Thursday, which happened as U.S. troops were screening people hoping to enter, once again underscored the human toll of the war — both for Afghans, the overwhelming majority of the victims, and for the American families who lost loved ones sent to fight it.

The 13 American military personnel who were killed came from across the country, from California to Wyoming to Tennessee, and had an average age of just over 22. Eleven were Marines, one was a Navy medic and another was in the Army.

About 113,500 people, most of them Afghans, have been evacuated since Aug. 14, a Pentagon official said, the day before the Taliban seized Kabul. On Saturday, about 1,400 people were still at the airport, having been screened and booked for flights, Pentagon officials said.

Hundreds of thousands of Afghans are still thought to be trying to flee the country. Mr. Biden and other global leaders have acknowledged that many will not get out before the deadline.