The FBI is investigating the explosion at a California fertility clinic as an act of terrorism

The person believed responsible for an attack targeting a Southern California fertility clinic Saturday posted rambling online writings before an explosion that investigators are treating as an act of terrorism, according to a law enforcement official.

The suspect, who died in the explosion that tore through the clinic and rattled the upscale California city of Palm Springs, also attempted to record video or stream the attack, said the official, who was not authorized to discuss details of the attack and spoke on condition of anonymity to The Associated Press.

“Make no mistake: This is an intentional act of terrorism,” Akil Davis, the head of the FBI’s Los Angeles field office, told an evening news conference.

Authorities were still working to piece together a motive and build a chronology of events leading up to the attack. Though the FBI did not say how it had determined the explosion was terrorism, the writings left behind, in which the suspect communicated a belief that the world should not be populated, appear to shed light on the person’s state of mind and help explain investigators’ thesis that the attack was targeted and intentional.

Authorities have not released the identity of the person thought to be responsible but believe the individual died in a car explosion. Davis said investigators weren’t looking for anyone else.

Four others were injured but details of the severity of their injuries weren't shared.

A burned-out vehicle was seen in the parking lot behind the clinic after the blast, which caved in the building’s roof, sprayed debris across a five-lane road and shattered windows in businesses blocks away. The clinic was closed for the weekend, and the doctor who leads it told the AP its staffers were safe.

The blast gutted the American Reproductive Centers fertility clinic, housed in a single-story building along a five-lane street lined with palm trees.

Dr. Maher Abdallah, who leads the clinic, told the AP in a phone interview that the explosion damaged the practice’s office space, where it conducts consultations with patients. The clinic's IVF lab and stored embryos are offsite and were not damaged.

“Thank God today happened to be a day that we have no patients," Abdallah said.

Palm Springs Mayor Pro Tem Naomi Soto called the clinic “a place of hope.”

“This is a building that people go to to start or expand their families,” she said. “We acknowledge their pain and concern across the community for the patients and staff."

Rhino Williams, 47, said he was chatting with customers at a hotel restaurant he helps manage just over a block away when he heard a huge boom. Everything rattled, Williams said, and he sprinted to the scene to see if anyone needed help.

Williams covered his nose with his shirt as he smelled burning plastic and rubber. He said he saw a building had “blown out” into the street, with bricks and debris scattered everywhere, and he spotted a car’s front axle on fire in the parking lot.

It was the only car in the lot, said Williams, who ran into the building, calling out and peering behind the counter to see if anyone was inside. He did not hear a response and did not see anyone behind the counter.

Williams then ran around checking on other buildings. Multiple windows of the neighboring liquor store also were blown out. Once he saw authorities arrive, Williams headed back to the hotel, he said.

Steven Michael Chacon was in his car preparing to turn into a hospital across the street from the clinic when felt and heard a massive boom as the building was torn apart, sending a massive plume of black smoke into the air. Not knowing what happened, he exited his car to flee the scene. Glass was all over the ground, and he saw what appeared to be a body part.

“I got out of my car and then people started screaming, there were people bloody, there was glass everywhere,” he said.

Palm Springs, about a two-hour drive east of Los Angeles, is known for upscale resorts, golf courses and a history of celebrity residents.

The Trump administration condemned the attack.

“The Trump administration understands that women and mothers are the heartbeat of America,” Attorney General Pam Bondi said in a statement. “Violence against a fertility clinic is unforgivable.”

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Associated Press journalists Sejal Govindarao and Kathleen Ronayne contributed.