The United States and allies urged Afghans to move away from Kabul airport on Thursday due to the threat of a terror attack by Islamic State (IS/Daesh) militants.

In an alert issued on Wednesday evening, the U.S. embassy in Kabul advised citizens to avoid travelling to the airport and said those already at the gates should leave immediately, citing unspecified “security threats”.

In a similar advisory, Britain told people in the airport area to move away and its armed forces minister, James Heappey, said intelligence of a possible suicide bomb attack by Daesh had become “much firmer”.

“I can’t stress the desperation of the situation enough. The threat is credible, it is imminent, it is lethal. We wouldn’t be saying this if we weren’t genuinely concerned about offering Islamic State a target that is just unimaginable,” Heappey told BBC radio.

Australia also issued a warning for people to stay away from the airport while Belgium ended its evacuation operations because of the danger of attack.

The Dutch government also issued a warning and said it expected to carry out its last evacuation flight on Thursday, leaving behind some who are eligible to travel to the Netherlands.

The Taliban, whose fighters are guarding the perimeter outside the airport, are enemies of the Afghan affiliate of Islamic State, known as Islamic State Khorasan (ISIS-K).

“Our guards are also risking their lives at Kabul airport, they face a threat too from the Islamic State group,” said a Taliban official, who spoke on condition of anonymity.