KABUL (REUTERS) - The United States carried out a missile strike on Islamic State militants in Kabul on Sunday (Aug 29), US officials said, as its forces at the capital's airport worked to complete a withdrawal that will end two decades of involvement in Afghanistan.

The officials, speaking on condition of anonymity, told Reuters the strike targeted suspected ISIS-K militants, a group that is an enemy of both the West and the Taleban and was responsible for a suicide bomb attack outside the airport gates last Thursday (Aug 26).

The attack by ISIS-K, a branch of Islamic State, killed at least 90 Afghans and 13 American troops as a huge evacuation operation was underway following the Taleban's seizure of Kabul on Aug 15.

The US officials said they were citing initial information and cautioned it could change.

Television footage showed black smoke rising into the sky but there was no immediate word on any casualties.

Two witnesses said the blast appeared to have been caused by a rocket that hit a house in an area to the northern side of the airport but there was no immediate confirmation.

The US strike took place while about 1,000 civilians waited at the airport to be flown out before the last troops leave, a Western security official told Reuters.

"We want to ensure that every foreign civilian and those who are at risk are evacuated today. Forces will start flying out once this process is over," the official said.

US President Joe Biden has said he will stick by his deadline to withdraw all U.S. troops from Afghanistan by Tuesday (Aug 31).

A US official told Reuters on Saturday that fewer than 4,000 troops remained at the airport.

The United States and allies have taken about 114,400 people - foreign nationals and vulnerable Afghans - out of the country in the past two weeks, but tens of thousands who want to go will be left behind.

The airlift - one of the biggest such evacuation operations ever - marked the end of a 20-year Western mission in Afghanistan that began when US-led forces ousted a Taleban government that had provided safe haven for the perpetrators of the Sept 11, 2001 attacks on the United States.

The final chapter came after the United States and the Taleban made a deal to end the foreign involvement by Aug 31 this year.

The Western-backed government and Afghan army melted away as Taleban fighters swept across the country and took control of Kabul.

"We tried every option because our lives are in danger. They (the Americans or foreign powers) must show us a way to be saved. We should leave Afghanistan or they should provide a safe place for us," said one woman outside the airport.

A Taleban official told Reuters the Islamist group had engineers and technicians ready to take charge of the airport.

"We are waiting for the final nod from the Americans to secure full control over Kabul airport as both sides aim for a swift handover," said the official, speaking on condition of anonymity.

Biden headed on Sunday to Dover Air Force Base to honour members of the US military killed in Thursday's attack as their remains were returned to the United States.

His national security adviser said Washington expected the Taleban to still allow safe passage for Americans and others to leave after the US military withdrawal is completed.

"The Taleban have both communicated privately and publicly that they will allow for safe passage," Jake Sullivan said in a CBS TV interview.

Financial and humanitarian crisis

The collapse of the government leaves an administrative vacuum that has led to fears of an economic crisis and widespread hunger.

Prices for commodities such as flour, oil and rice are rapidly rising and the currency is plunging, with money changers across the border in Pakistan already refusing to accept the afghani.

On Saturday, officials ordered banks to re-open and imposed a limit on withdrawals of US$200 or 20,000 afghani. Long queues formed outside bank branches of people trying to get money out.

Taleban spokesman Zabihullah Mujahid has said the difficulties will subside quickly once the new administration is up and running. But with its economy shattered by 40 years of war, Afghanistan is now facing the end of billions of dollars in foreign aid poured in by Western donors.

Mujahid said the Taleban would announce a full cabinet in the coming days. It had appointed governors and police chiefs in all but one of Afghanistan's 34 provinces, he said.

It also appealed to the United States and other Western nations to maintain diplomatic relations after withdrawing. Britain said that should happen only if the Taleban allow safe passage for those who want to leave and respect human rights.

The Taleban's 1996-2001 rule was marked by a harsh version of sharia, Islamic law, with many political rights and basic freedoms curtailed and women severely oppressed. Afghanistan was also a hub for anti-Western militants, and Washington, London and others fear it might become so again.

City calm

While Kabul's airport has been in chaos, the rest of the city has been generally calm. The Taleban have told residents to hand over government equipment including weapons and vehicles within a week.

The Western security official said crowds at the airport gates had diminished after a specific warning from the US government of another attack by ISIS-K, the branch of Islamic State in Afghanistan that is an enemy of both the West and the Taleban.

The United States said on Saturday it had killed two ISIS-K militants. Biden had vowed to hunt down the perpetrators of the explosion and said the strike was not the last.

The Taleban condemned the US drone strike, which took place in Nangarhar province, an eastern area that borders Pakistan. The airport attack added fuel to criticism Biden faced at home and abroad for the chaos.

He has defended his decisions, saying the United States long ago achieved its rationale for invading in 2001.

Britain's last military flight left Kabul on Saturday. Prime Minister Boris Johnson said Britain would not have wished to leave Afghanistan in such a manner.

But Richard Dannatt, a former head of the British army, said the British government need to investigate why it was so ill-prepared for the rapid fall of Afghanistan to the Taleban. "It is unfathomable why it would appear that the government was asleep on watch," Dannat told Times Radio.