US officials have warned American citizens in Afghanistan to stay away from the Kabul airport due to threats from the Islamic State group, multiple media outlets reported on Saturday.

The US Embassy in Afghanistan issued a security alert flagging “potential security threats outside the gates at the Kabul airport.”

“We are advising US citizens to avoid traveling to the airport and to avoid airport gates at this time unless you receive individual instructions from a US government representative to do so,” the alert said.

Media outlets, citing unnamed US officials, reported that the main threat was coming from ISIS’s Afghanistan branch.

US officials believe ISIS could launch an attack that would simultaneously harm Americans, and bruise the Taliban’s sense of control, The New York Times reported. The Times added that it was unclear whether ISIS was capable of such an attack.

The warnings come just one day after President Joe Biden promised that “any American who wants to come home, we will get you home.” He said more than 18,000 people have been evacuated since last month.

The new threats have frustrated American efforts to get evacuees to the Hamid Karzai International Airport and out of the country.

One official told the Associated Press that small groups of Americans will receive specific instructions on how to evacuate – namely, how to move to transit points where the military can greet them.

The Associated Press reported that the specifics of the ISIS threat were unclear, but officials described the threat as significant.

The scene around the airport Saturday morning was chaotic and desperate. Thousands – including children – were seen on video in a crushing crowd outside the airport gates, some pressed up against a barbed-wire fence.

The evacuations continued on Saturday, but the chaos meant that the flights had to depart before they were full.

Meanwhile, German and US forces joined in a gun battle Monday, 23rd at Kabul airport after Afghan guards and unknown assailants exchanged fire, with one guard killed, the German army said.

“This morning at 4.13 am, there was an exchange of fire between Afghan guards and unknown assailants at the North Gate of Kabul airport. An Afghan guard was killed, three others injured,” said the German army on Twitter.

“American and German forces participated in further exchange of fire,” it said, adding that no German soldiers were injured.

Kabul airport has seen chaotic scenes as tens of thousands of foreigners and Afghans seek to flee Afghanistan after the Taliban swept back to power more than a week ago.

The German army has since flown more than 2,500 people out using military planes.