KHOST, Afghanistan—The muezzin had just called for the morning prayer when soldiers brandishing guns jumped off their Toyota Hiluxes, surrounded Noor Walli Khan's house, knocked down the door, and entered the dark rooms where his family slept.

Minutes later, they had tied everyone's hands and feet and started pouring gasoline over the family's only car. Khan, 42, watched as the vehicle went up in flames. His children hid in the rooms left devastated by the raiders.

The surprise raid was the handiwork of the Khost Protection Force (KPF), a unit of Afghan soldiers trained, equipped, and funded by the CIA, operating mainly in the eastern province of Khost. The KPF's U.S.-directed mission: Root out anyone remotely suspected of al Qaeda or Taliban ties.