Nine members of one family - including six children - were killed in a US drone strike targeting a vehicle in a residential neighborhood of Kabul, a relative of the dead told a local journalist working with CNN.

The US carried out a defensive airstrike in Kabul, targeting a suspected ISIS-K suicide bomber who posed an "imminent" threat to the airport, US Central Command said Sunday.

The youngest killed was a 2-year-old girl, according to a brother of one of those killed. They were "an ordinary family," he said. "We are not ISIS or Daesh and this was a family home - where my brothers lived with their families."

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

"All the neighbors tried to help and brought water to put out the fire and I saw that there were five or six people dead," a neighbor told CNN. "The father of the family and another young boy and there were two children. They were dead. They were in pieces. There were [also] two wounded."

The US military acknowledged later Sunday that there are reports of civilian casualties following the strike.

"We know that there were substantial and powerful subsequent explosions resulting from the destruction of the vehicle, indicating a large amount of explosive material inside that may have caused additional casualties. It is unclear what may have happened, and we are investigating further," Capt. Bill Urban, spokesman for US Central Command, said in a statement.

"We would be deeply saddened by any potential loss of innocent life," he added.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 targeting the ISIS-K terror group in the space of three days. A US official confirmed the location of the strike as being in Kabul's Khaje Bughra neighborhood.

"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," 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 Taliban, which is now in control of Afghanistan, condemned the strike later Sunday, saying the US had violated the country's sovereignty.

Bilal Kareemi, a Taliban spokesperson, told CNN that it was "not right to conduct operations on others' soil" and that the US should have informed the Taliban. "Whenever the US conducts such operations, we condemn them," he said.

How the strike happened

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 earlier Sunday 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.

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.

US Secretary of Defense Lloyd Austin said in a statement that the 13 would be remembered as heroes. "These men and women made the ultimate sacrifice so that others could live," he said.

ISIS in Khorasan, known as ISIS-K, has claimed that an ISIS 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.

Vulnerable people left behind

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 Islamist 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.