U.S. officials have cited Islamic State as among possible attackers, a threat that national security advisor Jake Sullivan has said the U.S. is “laser-focused” on countering.

In Afghanistan, the group is thought to have only a small footprint, having been driven from its strongholds in the country’s east two years ago.

But its extremist ideology and the pitiless methods it has used to subdue civilians under its control — combined with its rivalry with the Taliban — pose a distinct threat, officials have warned.

In addition to the danger of an opportunistic terrorist attack, those braving the increasingly dangerous crush outside the gates have encountered intimidation and beating by Taliban fighters manning the barricades.

And even once people make it through the gate, processing delays sharply winnow the numbers of people cleared to board planes.