The US military launched a drone strike on an ISIS-K target in Afghanistan on Saturday, less than 48 hours after a devastating suicide bombing claimed by the group killed at least 169 Afghans and 13 US service members at Kabul airport.
US Central Command said the strike was carried out against an ISIS-K member in eastern Nangahar province who was believed to be involved in planning attacks against the US in Kabul.
One person was killed in the strike and Central Command spokesman Capt William Urban said there were no known civilian casualties.
On Saturday evening, the Pentagon said it would continue to search for more ISIS-K targets, without elaborating.
There is a high likelihood of further ISIS-K attacks around the airport, the Pentagon said.
US and international forces and are involved in an uneasy co-ordination effort with the Taliban in the continuing evacuation operation. About 111,000 people have been flown out of the country since August 14.
About 5,400 US citizens have been taken out of Afghanistan, Pentagon spokesman John Kirby said.
Last week, US Secretary of State Antony Blinken said about 6,000 American civilians, including embassy staff, aid workers and journalists, were in the country at the start of the evacuation.
On Friday, it was reported that a group of US Special Forces veterans had been conducting high-risk missions beyond the airport perimeter to rescue stranded Afghan allies and their families trying to evade Taliban checkpoints to reach the airport. The operation was known as Pineapple Express.
But co-ordination with the Taliban appeared to be holding on Saturday night and members of the militant group entered Kabul airport on Saturday, before an expected handover of the site when evacuation efforts end.
It remains to be seen whether the Taliban or international forces can stop another ISIS-K attack. US officials said all Americans should leave the airport immediately, following Thursday's bombing.
The air strike fulfilled a vow President Joe Biden made on Thursday, when he said the perpetrators of the attack would not be able to hide.
“We will hunt you down and make you pay,” he said.
On Friday, Pentagon leaders said they were prepared for whatever retaliatory action Mr Biden ordered.
“We have options there right now,” said Maj Gen Hank Taylor of the Pentagon’s Joint Staff.
On Friday, Mr Biden was told to expect another deadly attack in the closing days of a frantic US-led evacuation effort in Afghanistan.
White House press secretary Jen Psaki said Mr Biden's national security team offered a grim outlook.
"They advised the president and vice president that another terror attack in Kabul is likely, but that they are taking maximum force protection measures at the Kabul airport,” Ms Psaki said.
That echoed what the Pentagon has been saying since Thursday's bombing that pushed the White House deeper into crisis over a chaotic and deadly conclusion to a war that began nearly 20 years ago.
Late Friday, the State Department again urged Americans to stay away from airport gates, including “the New Ministry of Interior gate”.
Few new details were known about the attack a day later, but the Pentagon corrected its initial report that there had been suicide bombings at two locations.
It said there was only one bombing at or near the Abbey Gate, with the attack followed by gunfire.
The initial report of a second bombing at the nearby Baron Hotel proved to be false, Maj Gen Taylor. He attributed the mistake to initial confusion.
Based on a preliminary assessment, the suicide vest used in the attack carried about 11 kilograms of explosives and was loaded with shrapnel, a US official said.
A suicide bomb typically carries between 2kg and 4.5kg of explosives, the official said.
Mr Biden also faces the long-term problem of containing an array of potential extremist threats in Afghanistan.
In an Oval Office appearance on Friday, Mr Biden again expressed his condolences to victims of the attack.
The return of the remains of US military personnel in the coming days will provide painful and poignant reminders not only of the devastation at Kabul airport, but also the costly way the war is ending.
The Marine Corps said 11 of the 13 Americans killed were marines. One was a navy sailor and one an army soldier.
Their names have not been released pending notification of their families, a process Mr Kirby said involved “difficult conversations”.
Still, sorrowful details of those killed were starting to emerge. One marine from Wyoming was on his first tour in Afghanistan and his wife is expecting a baby in three weeks; another was a 20-year-old man from Missouri whose father was devastated by the loss.
A third, a 20-year-old from Texas, had joined the armed forces after leaving high school.
Mr Biden ordered US flags to half staff across the country in honour of the 13.
They were the first US service members killed in Afghanistan since February 2020, the month the Trump administration struck an agreement with the Taliban.
The deal called for the militants to halt attacks on US personnel in exchange for an agreement from Washington to remove all American troops and contractors by May 2021.
Mr Biden announced in April that he would have all forces out by September.
Ms Psaki said the next few days of the mission to bring Americans and others, including vulnerable Afghans fleeing Taliban rule, out of Kabul “will be the most dangerous period to date”.
Mr Biden has set Tuesday as the deadline for completing the operation.
The White House said that as of Friday morning, about 12,500 people were flown out of Kabul in the past 24 hours on US and coalition aircraft. In the 12 hours that followed, another 4,200 people were flown out of Kabul.
Ms Psaki said about 300 US citizens departed and the State Department was working with about 500 more who wanted to leave.
Mr Kirby said the US military was monitoring credible, specific ISIS threats “in real time”.
“We certainly are prepared and would expect future attempts,” he said.
He declined to describe details of any additional security measures being taken, including those introduced by the Taliban, around the gates and the perimeter of the airport.
He said there were fewer people in and around the gates on Friday.
The AP contributed to this report.