A 25-year-old man the FBI believes was responsible for an explosion that ripped through a Southern California fertility clinic left behind “anti-pro-life” writings before carrying out an attack investigators called terrorism,

The explosion on Saturday morning, which occurred in or near a vehicle less than a mile from downtown Palm Springs, Calif., was “an intentional act of terrorism,” the F.B.I. said.

A law enforcement official says the person believed responsible for an explosion at a California fertility clinic posted online ramblings including a belief that the world should not be populated.