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The FBI descended on the Four Seasons Hotel in L.A. ... 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.
We're told agents seized a cellphone, 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. They wanted money in exchange for the phantom tape.
We believe the same woman has called media outlets -- including TMZ -- posing as Kris Kardashian.
