A bomb explosion outside a California fertility clinic has killed one person and injured four others in an ?intentional act of terrorism?, FBI officials have said.

The blast happened just before 11:00 local time (19:00 BST) less than a mile from downtown Palm Springs, near several businesses including the American Reproductive Centers (ARC). The clinic said no-one from the facility was harmed.

The FBI later said It had ?a person of interest? in its investigation, but officers were ?not actively searching? for the suspect.

Michael Beaumier, a witness, said he was knocked off his bike by the blast. ?It was that big of an explosion and I could hear windows shattering all around me,? he said.

Rhino Williams, who was at his restaurant nearby, told the BBC he initially thought the explosion was a plane or helicopter crashing.

He said he ran to the scene to see if he could help, finding a badly damaged building with walls blown out and the front axle of a car on fire in the car park.

?That?s all that was left of it,? Mr Williams said. He also saw an iPhone on a tripod still standing in the car park, as if it was set to film or stream the explosion.

Mr Williams said he rushed through the building shouting for any injured people ? but did not find any. A few minutes later first responders arrived.

Nima Tabrizi, another witness, said he heard a ?big boom?, a large cloud of smoke and the front of the clinic ?completely blown out?.

The FBI said In a Saturday briefing that it was a deliberate attack.

?This was an intentional act of terrorism. As our investigation will unfold we will determine if it?s international terrorism or domestic terrorism,? said Akil Davis, the head of the FBI's Los Angeles field office.

Palm Springs police chief Andy Mills said the blast damaged several buildings, some severely.

He added that the identity of the person who was killed was not known.

The ARC in Palm Springs said the explosion occurred in the car park near its building.

Palm Springs Mayor Ron De Harte told BBC?s US partner CBS News that the source of the explosion ?was in or near the vehicle?.

The fertility clinic said their lab, including all eggs and embryos, remained ?fully secure and undamaged?.

?We are heavily conducting a complete safety inspection and have confirmed that our operations and sensitive medical areas were not impacted by the blast,? the clinic said in its statement.

But Dr Maher Abdallah, who runs the clinic, told the Associated Press that the clinic?s office was damaged.

?I really have no clue what happened,? he said. ?Thank God today happened to be a day that we have no patients.?

According to its website, the ARC clinic is the first full-service fertility centre and in vitro fertilisation lab (IVF) in the Coachella Valley.

It offers services like fertility evaluations, IVF, egg donation and freezing, reproductive support for same-sex couples and surrogacy.

California Governor Gavin Newsom said the state was co-ordinating with local and federal authorities, while US Attorney General Pam Bondi said she had been briefed on the incident. (BBC)

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