Hundreds of students and alumni of American University of Kabul gathered at a safe house on Sunday and boarded buses in what was supposed to be a final attempt at evacuation on U.S. military flights, students and alumni said.

But after seven hours of waiting for clearance to enter the airport gates and driving around the city, the group met a dead end: Evacuations were permanently called off. The airport gates remained a security threat, and civilian evacuations were ending Monday.

“I regret to inform you that the high command at HKIA in the airport has announced there will be no more rescue flights,” said an email sent to students from the university administration on Sunday afternoon, which was shared with The New York Times.

The email asked the 600 or so students and alumni to return home.