KABUL — The United States carried out a defensive airstrike in the Afghan capital, Kabul, targeting a suspected Daesh (ISIS-K) suicide bomber who posed an "imminent" threat to the airport, US Central Command said Sunday.

US forces have been racing to complete their evacuation operation before Tuesday's deadline and under the threat of a new terror attack on Hamid Karzai International Airport in Kabul.

A suicide bombing outside the airport gates on Thursday killed 13 US service members and at least 170 others. Sunday's drone strike on a vehicle is the second by US forces targeted the ISIS-K terror group in the space of three days.

"US 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," said US CENTCOM spokesman Capt. Bill Urban.

"We are confident we successfully hit the target. Significant secondary explosions from the vehicle indicated the presence of a substantial amount of explosive material."

The vehicle that was targeted by the US in Sunday's airstrike on Kabul was next to a building and contained one suicide bomber, a US official told CNN. It remains unclear if the vehicle was intended to be a car bomb, or if the suicide bomber was using it for transport. "It was loaded up and ready to go," the official tells CNN.

A Pentagon official told CNN that according to initial reports, the target was a vehicle believed to be containing multiple suicide bombers. The threat could also have been a car bomb or someone with a suicide vest, he said, citing initial reports.

Urban said the US military was "assessing the possibilities of civilian casualties, though we have no indications at this time" and would remain vigilant against potential future threats.

Neighbors and witnesses at the scene of the drone strike in Kabul told CNN that several people were killed, including children.

One man told a journalist working with CNN who visited the compound that "a rocket hit and six people were in there who have been killed. There was a car inside." The journalist was not allowed to enter the compound.

Another man said that he heard the sound of a rocket and gained access to the scene from a neighbor's house. "First we managed to remove a 3- to 4-year old child. The fire and smoke had engulfed the whole area," he said.

He added that "three people were inside the car" and three others were outside the car. The injured, who included children, were taken to the hospital, he said.

US President Joe Biden said Saturday that military commanders had advised that "another terrorist attack on Kabul's airport is "highly likely in the next 24-36 hours," and the US Embassy in Kabul warned all US citizens to leave the airport area immediately.

The White House said Sunday morning that about 2,900 people were evacuated from Kabul from 3 a.m. ET Saturday to 3 a.m. ET Sunday. Those evacuations were carried out by 32 US military flights and nine coalition flights.

The mission is clearly winding down, with fewer people brought out than during the same time period on preceding days.

Biden traveled to Dover Air Force Base in Delaware on Sunday to mourn with the families of the 13 US service members killed in Thursday's attack as their bodies were brought back to US soil.

ISIS in Khorasan, known as ISIS-K, has claimed that a Daesh militant carried out the suicide attack, but provided no evidence to support the claim. US officials have said the group was likely behind the bombing.

On Saturday, the Pentagon said two "high profile" ISIS targets had been killed and another injured in a US drone strike late Friday in Jalalabad, in Afghanistan's eastern Nangarhar province, in a retaliatory strike for Thursday's attack.

After a desperate, two-week effort to evacuate their citizens and Afghan allies from the country following the Taliban's seizure of power, Western governments now face the challenge of how to deal with an militant group they've spent the past two decades fighting.

French President Emmanuel Macron has said he intends, alongside the United Kingdom, to submit a resolution to an emergency session of the UN Security Council (UNSC) that would focus on the creation of a "safe zone" in Kabul for Afghans leaving the country.

"Our draft resolution aims to define, under UN protection, a safe zone in Kabul that would allow humanitarian operations to continue," Macron told French newspaper Journal du Dimanche, adding that he intends to "maintain pressure on the Taliban" in doing so. The UNSC session is due to convene Monday.

US national security adviser Jake Sullivan said Sunday that the Biden administration was committed to a "safe passage" of Americans and Afghans who helped the US government after the withdrawal deadline.

"Aug. 31 is not a cliff. After Aug. 31, we believe that we have substantial leverage to hold the Taliban to its commitments to allow safe passage for American citizens, legal permanent residents and the Afghan allies who have travel documentation to come to the United States,” Sullivan told CNN.

“We will use that leverage to the maximum extent and we will work with the rest of the international community to make sure the Taliban does not falter on these commitments.”

Roughly 250 Americans who are attempting to leave Afghanistan remain in the country, according to new figures from a US State Department spokesperson. About 50 evacuations have taken place in the past day, bringing the total number of American citizens evacuated to 5,500.

The US State Department, along with governments from numerous other countries, released a statement Sunday saying they would hold the Taliban to their promises that they would allow people to leave the country after Aug. 31.

"We will continue issuing travel documentation to designated Afghans, and we have the clear expectation of and commitment from the Taliban that they can travel to our respective countries," the statement said. — CNN