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7:40 PM PT -- Jermaine Jackson responded via Twitter to the missing person's report, saying in part, "No-one is being "blocked" from speaking with Mother. She is merely an 82-year-old woman following doctor's orders to rest-up and de-stress, away from phones and computers. Everyone has been well aware of this within the family, but I would like to reiterate my reassurance to the outside world that Mother is fine."

11:40 AM PT -- A source tells the AP that Katherine is with her daughter Rebbie and has been prescribed rest by a physician.

9:30 AM PT -- Katherine's lawyer released a statement, saying in part, "Concerned family members, particularly Michael's children, have since made ongoing pleas to those believed to have knowledge of her location for information regarding her whereabouts. The only reports provided have been both conflicting and confusing -- especially those pertaining to the status of Katherine Jackson's health. When Michael's children last saw their grandmother on July 15, 2012, she was in great health physically as well as mentally."

She continued, "Prince, Paris, and Blanket are the light of Katherine Jackson's life, as she is to those children. Out of concern for Mrs. Jackson's well-being and in an effort to ensure her being safely reunited with her grandchildren as soon as possible, a report was filed on Saturday with the Sheriff's Department who will be investigating this matter."

4:44 AM PT -- The Los Angeles County Sheriff's Department issued a release that says, "Katherine Jackson is reportedly with family members. Late Saturday night, a different family member reported that he was unable to speak with her and is concerned for her well being. Deputies are continuing to make efforts to reach her and ask that she contact the Malibu / Lost Hills Sheriff’s Station of the Los Angeles County Sheriff’s Department."

Katherine Jackson has been reported missing by her nephew late Saturday night ... law enforcement sources tell TMZ.

According to our sources, a nephew of Katherine's filed a missing person's report with the L.A. County Sheriff's Department after her grandchildren had been unable to reach her for over a week.

Jermaine Jackson tweeted earlier this week that Katherine was in Arizona resting up on doctor's orders. But early this morning, Paris Jackson tweeted, "yes, my grandmother is missing. i haven't spoken with her in a week i want her home now."

She followed that up with a plea for people to call the authorities if they see her, then added, "the same doctor that testified on behalf of dr murray saying my father was a drug addict (a lie) is caring for my grandmother... just saying."

Katherine Jackson's lawyer told CNN she has never gone more than 24 hours without speaking to her grandchildren.

As TMZ previously reported, the Jackson family has been feuding of late ... with Randy, Jermaine, Tito, Rebbie and Janet Jackson seeking to have the executors of the Michael Jackson Estate resign from their positions.