"The unmanned airstrike occurred in the Nangarhar Province of Afghanistan. Initial indications are that we killed the target," said Captain Bill Urban of the Central Command.

"We know of no civilian casualties," he added in a statement annoucing the first reported US strike since the attack.

The strike, launched from outside of Afghanistan, came as the airlift of evacuees from Kabul airport continued under much-heightened security after Thursday's attack.

At least 78 people were killed, including 13 US troops, when a suicide attacker exploded a bomb in the dense crowd in front of the aiport's Abbey Gate. Some media reported that fatalities numbered close to 200.

US officials said gunmen opened fire after the explosion, adding to the carnage.

The attack was carried out by the violent Afghan arm of the Islamic State group.

Following the attack US President Joe Biden vowed retaliation.

"To those who carried out this attack as well as anyone who wishes America harm, know this: We will not forgive. We will not forget. We will hunt you down and make you pay," Biden said Thursday.

On Friday afternoon Pentagon spokesman John Kirby said they believe the group planned to strike the airlift again.

"We still believe there are credible threats... specific, credible threats," he said.