Kabul, Afghanistan – The US military said it carried out an airstrike in the Afghan capital on Sunday to avert an "imminent" threat to Kabul airport from a local offshoot of the Islamic State terrorist militia.

A drone successfully hit a car belonging to the terrorist group known as called Islamic State Khorasan, or ISIS-K, according to the US military.

The strike came as US President Joe Biden warned of an "extremely dangerous" situation in Kabul as the US was preparing to pull out its remaining troops from the airport.

Because there were "significant secondary explosions" after the drone strike, it was assumed that there must have been a large quantity of explosives in the vehicle, US officials said.

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The US military initially said there were no indications of civilian casualties, but later said it was aware of reported civilian deaths and was looking into them.

"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," US Central Command spokesperson Bill Urban said.

"We would be deeply saddened by any potential loss of innocent life."

Local television station ArianaNews meanwhile cited eyewitnesses saying that six people, including four children, were killed when a mortar shell hit a private house in Kabul's 15th police district.

Two vehicles and parts of the house were destroyed. It was not immediately clear if these casualties might have been caused by the US airstrike rather than a mortar shell. The airport is also located in the 15th police district.

CNN reported that nine members of one family were killed in the strike, including six children. The US broadcaster cited relatives in Kabul.

The situation in Kabul remains volatile after ISIS-K claimed responsibility for Thursday's airport bombing that killed dozens of people, including 13 US soldiers.

Monday morning saw the violence continue with as many as five rockets launched toward the Kabul airport. Reuters reported that at least some of them were stopped by a US missile defense system. At this time, there are no reported US casualties.

US Secretary of State Antony Blinken told broadcaster NBC that it was "not likely" that the United States would have any diplomatic representation in Afghanistan from September onwards.

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Biden's national security adviser Jake Sullivan meanwhile told broadcaster CBS that the current plan is not to have an embassy in Kabul.

Blinken stressed, however, that the US would help people leave Afghanistan beyond September.

US troops have begun their withdrawal from Kabul, with some 5,000 soldiers set to fly out by Tuesday.

The US State Department said it is also working to bring about 250 US citizens still in Afghanistan to safety. So far, a total of 5,500 US citizens have been evacuated from Afghanistan since the militant Islamist Taliban took power in mid-August, officials say.

US diplomats are also in contact with about 280 people who say they are US citizens but have so far not given any information about their planned departure or who say that they want to stay on.

Around 2,900 people were flown out of the airport on 32 flights in the past 24 hours, a White House spokesperson said on Sunday, while nine allied aircraft had evacuated around 700 people.

Since the start of the withdrawal mission in mid-August, the US and its partners have flown out a total of 114,000 people.

The number of people flown out per day has recently dropped significantly due to the beginning of the US withdrawal and the suspension of rescue flights by allies.

From Tuesday to Wednesday, for example, about 19,000 people were evacuated in the space of 24 hours. Meanwhile, the number of US Air Force flights declined only slightly, suggesting that more US soldiers and equipment are now being flown out.

Leaders of the Taliban have assured several countries that the militant Islamist group will continue to allow their citizens and military forces to leave the country.

"We have received assurances from the Taliban that all foreign nationals and any Afghan citizen with travel authorization from our countries will be allowed to proceed in a safe and orderly manner to points of departure and travel outside the country," reads a joint statement from more than 20 countries, including the US, the UK, and Germany.

In recent days, several senior Taliban members had publicly asserted that Afghans could continue to leave the country through legal channels.