European nations offered stark warnings Thursday about the waning days of a massive airlift to bring people out of Taliban-controlled Afghanistan, with a British official saying an “imminent attack” could target Kabul’s international airport.

France said it would halt its evacuations Friday while Denmark said its last flight had already left Kabul’s airport, which has seen thousands throng around it in the days since the Taliban took the capital.

Read:US says 1,500 Americans may still await Kabul evacuation

Overnight, new warnings emerged from Western capitals about a possible threat from Afghanistan’s Islamic State affiliate, which likely has seen its ranks boosted by the Taliban freeing prisoners across the country. Already, military cargo planes leaving Kabul airport have launched flares to disrupt any potential surface-to-air missile fire as fleeing Afghan troops abandoned heavy weapons and equipment across the country in their collapse following America’s withdrawal of troops.

British Armed Forces Minister James Heappey told the BBC on Thursday there was ”very, very credible reporting of an imminent attack” at the airport, possibly within “hours.”

Heappey conceded that people are desperate to leave and “there is an appetite by many in the queue to take their chances, but the reporting of this threat is very credible indeed and there is a real imminence to it.”

Read: What's happening with Afghanistan evacuations?

“We will do our best to protect those who are there,” he said. “There is every chance that as further reporting comes in, we may be able to change the advice again and process people anew but there’s no guarantee of that.”

Outside of a missile attack, troops have been worried about the uncontrolled, teeming crowds outside the airport. While the Taliban and others have tried to control them, there’s no formal screening process on the way the airport as there was under Afghanistan’s former government. That means someone carrying a suicide bomb could slip through — or an explosives-laden vehicle could barrel through.

On Wednesday, the U.S. Embassy in Kabul issued a security alert warning American citizens away from three specific airport gates, but gave no further explanation.

Senior U.S. officials said the warning was related to ongoing and specific threats involving the Islamic State and potential vehicle bombs. The officials spoke on condition of anonymity because they were not authorized to discuss ongoing military operations.

Read: US troops surge evacuations out of Kabul but threats persist

French Prime Minister Jean Castex told French radio RTL on Thursday that “from tomorrow evening onwards, we are not able to evacuate people from the Kabul airport” due to the Aug. 31 American withdrawal.

Meanwhile, Danish defense minister Trine Bramsen bluntly warned: “It is no longer safe to fly in or out of Kabul.” Denmark’s last flight, carrying 90 people plus soldiers and diplomats, already had left Kabul.