United States military commanders believe that another terror attack on the Kabul airport was highly likely in the next 24 to 36 hours, President Joe Biden said on Saturday.

Hours later, the US embassy in Afghanistan issued a security alert, asking Americans to leave the vicinity of Kabul airport immediately following a “specific, credible threat”. It also asked citizens to avoid travelling to the airport and avoid all gates.

After a briefing from his national security team, Biden said that the US drone strike targeting the Islamic State-Khorasan group, which claimed responsibility for the bombing at the Kabul airport on Thursday, would not be the last such action.

Over 100 people, including 13 US service members, were killed when a bomb exploded in front of the airport’s Abbey Gate.

In a statement, Biden on Saturday again vowed to punish those responsible for the attack.

“We will continue to hunt...make them pay,” he said. “Whenever anyone seeks to harm the United States or attack our troops, we will respond. That will never be in doubt.”

The president said that the situation in Kabul continues to be extremely dangerous. Biden added that he had asked commanders to “take every possible measure to prioritise force protection”.

US troops and its allies have been scrambling to evacuate citizens and at-risk Afghans ahead of the August 31 deadline to exit Afghanistan. As of Saturday, an official told Reuters that there were fewer than 4,000 American troops at the Kabul airport, down from 5,800 at the peak of the evacuation operation.

Despite the threat of another attack, Biden said his military commanders had assured him that they had plans to protect Americans on the ground while completing the evacuation.

The last British flight evacuating civilians from Afghanistan left Kabul on Saturday. According to reports, many Afghans are also trying to leave the country through the border with Pakistan.