KABUL, Afghanistan (AP) — Potential Islamic State threats against Americans in Afghanistan are forcing the U.S. military to develop new ways to get evacuees to the airport in Kabul, a senior U.S. official said Saturday, adding a new complication to the already chaotic efforts to get people out of the country after its swift fall to the Taliban.

The official said that small groups of Americans and possibly other civilians will be given specific instructions on what to do, including movement to transit points where they can be gathered up by the military. The official spoke on condition of anony...