Authorities are now investigating whether the attack, which killed one person and injured others, was live-streamed.
An explosion killed a person and heavily damaged a fertility clinic on Saturday in the upscale California city of Palm Springs in what the FBI characterised as an "intentional act of terrorism".
Akil Davis, the head of the FBI's Los Angeles field office, said in the evening that the clinic was deliberately targeted, while declining to elaborate on how authorities have reached a conclusion on a motive.
Authorities were still working to confirm the identity of the person who died at the scene. Davis would not directly say whether that person was the suspect but said authorities were not searching for a suspect.
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Davis also said four people were hurt but provided no additional details on the severity of the injuries.
Authorities were also investigating the possibility that the explosion was being livestreamed.
The FBI said it was sent investigators, including bomb technicians, to the scene.
Palm Springs Police Chief Andy Mills said in a statement that the blast "appears to be an intentional act of violence" and several buildings were damaged, some severely.
"There has been one fatality, the person's identity is not known," Mills said.
The act was being investigated as a possible car explosion, according to two law enforcement officials briefed on the matter who insisted on anonymity to discuss preliminary information from an ongoing investigation.
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One of the officials told AP that investigators believe the person who died was likely the person who set off the explosion, but they cautioned that the investigation was still in its early stages.
Attorney General Pam Bondi said federal agents were working to learn more, adding, "Let me be clear: the Trump administration understands that women and mothers are the heartbeat of America. Violence against a fertility clinic is unforgivable".
The FBI's Los Angeles field office said via the social platform X that "investigators, bomb technicians & an evidence response team" were among assets that were deployed. Investigators from the Bureau of Alcohol, Tobacco, Firearms and Explosives were also assisting.
The city of Palm Springs said the explosion happened at 11 am and residents were asked to avoid the area around North Indian Canyon Drive near East Tachevah Drive.
Dr Maher Abdallah, who runs the American Reproductive Centers fertility clinic, confirmed that his facility was damaged. He told AP in a phone interview that all staffers were safe and accounted for. The explosion damaged the practice's office space, where it conducts consultations with patients, but the IVF lab and the stored embryos were spared.
"I really have no clue what happened," Abdallah said. "Thank God today happened to be a day that we have no patients."
Aerial video showed a burned-out car in a parking lot behind the building that housed the fertility clinic's office space. The blast caved in the roof and blew a wide debris field across a sidewalk and four lanes of the street on the other side of the structure.
Rhino Williams, 47, said he was chatting with customers at a restaurant he helps manage inside the Skylark Hotel 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 was in need of help.
Williams saw a large dark grey plume of smoke and 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.
He said it was the only car in the lot that he saw. He 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 to check on other buildings. Multiple windows of the neighbouring liquor store were also blown out, he said. Once he saw authorities arrive, he headed back to the hotel.
Nima Tabrizi, 37, of Santa Monica, said he was inside a cannabis dispensary nearby when he felt a massive explosion.
"The building just shook, and we go outside and there's massive cloud smoke," Tabrizi said. "Crazy explosion. It felt like a bomb went off. ... We went up to the scene, and we saw human remains."
Palm Springs is about a two-hour drive east of Los Angeles. Its known for upscale resorts, golf courses and a history of celebrity residents.
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