Authorities said Sunday that the suspect in Saturday's explosion at a California fertility clinic, which they described as an "intentional act of terrorism," was killed in the incident.

The blast gutted the single-storey American Reproductive Centers clinic in upscale Palm Springs, although a doctor told The Associated Press its staff were safe.

"Thank God today happened to be a day that we have no patients," Dr. Maher Abdallah, who leads the clinic, told the AP in a phone interview on Saturday.

Akil Davis, the head of the FBI's Los Angeles field office, said that all embryos at the facility were saved.

Investigators on Sunday said the suspect, identified as 25-year-old Guy Edward Bartkus, posted writings online and attempted to record the explosion, although authorities said the video failed to upload online. An official who was not authorized to discuss details of the attack spoke on condition of anonymity to The Associated Press.

The person believed responsible for the attack posted rambling online writings before the explosion, according to a law enforcement official.

"Make no mistake: This is an intentional act of terrorism," Davis told an evening news conference Saturday.