Afghans, hoping to leave Afghanistan, walk to the main entrance gate of Kabul airport in Kabul on August 28, 2021, following the Taliban stunning military takeover of Afghanistan. (WAKIL KOHSAR / AFP)

WASHINGTON -  US President Joe Biden warned on Saturday that another terror attack against Kabul airport could be "highly likely in the next 24-36 hours."

"The situation on the ground continues to be extremely dangerous, and the threat of terrorist attacks on the airport remains high. Our commanders informed me that an attack is highly likely in the next 24-36 hours," Biden said in a statement after meeting with his national security team.

Pentagon Press Secretary John Kirby said earlier in the day that the US forces on the ground had begun withdrawal from Kabul airport

"I directed them to take every possible measure to prioritize force protection, and ensured that they have all the authorities, resources and plans to protect our men and women on the ground," he added.

Thirteen US service members and some 170 Afghans were killed in a suicide bombing attack outside Kabul airport on Thursday. ISIS-K, a local affiliate of the Islamic State in Afghanistan, had claimed responsibility for the attack.

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In retaliation for the deadly attack, the US military on Friday launched a drone strike against the terror group in Nangarhar province of eastern Afghanistan, which killed two "high-profile" members and wounded another, according to the Pentagon.

"This strike was not the last," Biden said in the statement. "We will continue to hunt down any person involved in that heinous attack and make them pay."

Biden set Aug 31 as the deadline to end US military mission in Afghanistan. Pentagon Press Secretary John Kirby said earlier in the day that the US forces on the ground had begun withdrawal from Kabul airport.

The United States has been scrambling to evacuate Americans and its Afghan partners from the country since the Taliban entered Kabul on Aug 15. The White House said on Saturday that around 111,900 people had left Afghanistan since Aug 14.  

The Taliban condemned the overnight US drone strike, which took place in Nangarhar Province, an eastern area that borders Pakistan.

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"The Americans should have informed us before conducting the air strike. It was a clear attack on Afghan territory," a Taliban spokesman told Reuters, adding that two women and a child were wounded in the attack.

The Taliban have said they have arrested some suspects involved in the airport blast.

Spokesman Zabihullah Mujahid also said the Taliban would take over the airport "very soon", after US forces withdraw, and announce a full cabinet in the coming days.

Mujahid told Reuters the group had appointed governors and police chiefs in all but one of Afghanistan's 34 provinces and would act to solve the country's economic problems.

A US official told Reuters on Saturday there were fewer than 4,000 troops left at the airport, down from 5,800 at the peak of the evacuation mission. 

The Taliban, facing the loss of billions of dollars of aid for the country, urged the United States and other Western nations to maintain diplomatic relations after their withdrawal.

Dangerous Final Days

The White House said the next few days were likely to be the most dangerous of the evacuation operation. The United States and allies have taken about 113,500 people out of Afghanistan in the past two weeks, it said.

US military and allied countries' flights carried fewer people on Saturday as Washington prepared to end its mission.

With another attack against Kabul airport a near certainty, according to US officials, the State Department reiterated its warning to Americans to immediately leave the area due to "a specific, credible threat", including the South gate, new Ministry of Interior, and gate near Panjshir petrol station.

The last British flight evacuating civilians from Afghanistan left Kabul on Saturday. British troops would take small numbers of Afghan citizens with them as they leave this weekend, a defense ministry spokesperson said. Armed forces chief Nick Carter said hundreds of people who had worked with Britain would not make it through.

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In the Pentagon's strike on militant suspects in Nangarhar, a US official said on Friday that an MQ-9 Reaper unmanned aircraft flown from the Middle East targeted an Islamic State militant who was planning attacks and was in a car with an associate.

Residents of Jalalabad, the provincial capital, said they had heard several explosions around midnight and community elder Malik Adib said three people were killed and four were wounded in an air strike, adding that he had been summoned by the Taliban investigating the incident.

"Women and children are among the victims," said Adib, though he did not have information about their identity.

The US military said in a statement that it knew of no civilian casualties.

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

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The airport attack added fuel to criticism Biden faced at home and abroad for the chaos after Afghanistan's government and military collapsed before a lightning Taliban advance. He has defended his decisions, saying the United States long ago achieved its rationale for invading in 2001.