The FBI descended on the Four Seasons Hotel in Bev Hills ... on the hunt for a woman they believed was making death threats and harassing phone calls to Kris Jenner and her family.
FBI sources confirm ... agents obtained a search warrant targeting a suspect -- a black female who drives a 2004 silver Toyota Corolla -- the woman they believe is behind the threats.
The agents seized a cell phone, laptop, iPad and iPod Touch when they rooted through the woman's hotel room Friday ... but she was not arrested.
TMZ broke several stories in the past ... about a woman who was incessantly calling Kris Jenner and making various threats. She sometimes called as many as 300 times a day, threatening to release a sex tape starring Kris and Bruce Jenner. She wanted money in exchange for the phantom tape.
We believe the same woman has called media outlets -- including TMZ -- posing as Kris Jenner.