One person is dead and at least four are injured in the desert oasis of Palm Springs, Calif., after a bomb exploded on Saturday morning outside a fertility clinic, damaging buildings and leaving windows shattered across several blocks in what authorities called a terrorist attack.

“This explosion was significant,” said Akil Davis, the assistant director in charge of the F.B.I.’s Los Angeles Field Office. “Make no mistake, this is an intentional act of terrorism.” He added that officials believed the clinic was specifically targeted.

Mr. Davis said that the bureau had begun one of the largest bombing investigations ever in Southern California and that it was not yet clear whether the event had been an act of domestic or international terrorism. Authorities have identified a person of interest but did not name the person on Saturday afternoon. They also did not say whether the person who died was connected to the blast. Mr. Davis said that “we are not actively out searching for a suspect.”

The explosion was in or near a vehicle parked by the clinic, according to the mayor, Ron deHarte. But many other details were unclear, including the vehicle’s make and model. All that was left of it at the scene was an axle, authorities said.

The bombing was an isolated incident and the community was no longer at risk, Andy Mills, the Palm Springs police chief said.

Reports of a loud boom and images of broken glass and billowing smoke began to be shared on social media around 11 a.m. local time. The blast area extended for blocks, and some buildings were severely damaged, with shattered windows visible in many restaurants, shops and apartment buildings throughout the city’s downtown.

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