A member of the ruling family of Ras al-Khaimah, one of seven states that make up the United Arab Emirates, has been held "without charge" for days, his son said on Wednesday.
Sheikh Sultan Al-Qassimi, a first cousin of the emir who heads the local branch of the Islamist group Al-Islah, was arrested on Friday by "armed men in civilian clothing," his son Sheikh Abdullah told AFP by telephone.
Sheikh Sultan "is being held in a room secured by guards at the governor's palace," the son said, condemning the absence of "any formal charges against him."
"He refuses to sign anything or give any statements to the authorities as long he is being detained in this manner," Sheikh Abdullah said, a day after visiting his father in custody.
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He said a family member had warned his father two weeks ago that he could be detained, adding: "We demand his immediate release."
A well-informed tribal source said Sheikh Sultan had been placed under "house arrest" following a "family" dispute within the Al-Qassimi clan.
He insisted there was no involvement by the UAE security services. "The issue is being resolved within the Al-Qassimi clan," he added.
In a statement posted on its website, the Al-Islah group condemned Sheikh Sultan's detention as an "unprecedented provocation".
Earlier this month, UAE authorities detained six members of Al-Islah and revoked their citizenship for alleged links to terrorism funding.