LONDON — In the telling of some American officials, the C.I.A. drone campaign in Pakistan has been a triumph with few downsides: In more than 300 missile attacks there since 2008, dozens of Qaeda and Taliban leaders have been killed, and the pace of the strikes, which officials frequently describe as “surgical” and “contained,” has dropped sharply over the past year.

But viewed from Miram Shah, the frontier Pakistani town that has become a virtual test laboratory for drone warfare, the campaign has not been the antiseptic salve portrayed in Washington. In interviews over the past year, residents paint a portrait of extended terror and strain within a tribal society caught between vicious militants and the American drones hunting them.

“The drones are like the angels of death,” said Nazeer Gul, a shopkeeper in Miram Shah. “Only they know when and where they will strike.”

Their claims of distress are now being backed by a new Amnesty International investigation that found, among other points, that at least 19 civilians in the surrounding area of North Waziristan had been killed in just two of the drone attacks since January 2012 — a time when the Obama administration has held that strikes have been increasingly accurate and free of mistakes.