Rached Ghannouchi, leader of Tunisia's biggest and most organised political party Ennahda, arrived for questioning by an investigating judge at an anti-terror centre as his supporters rallied outside the courthouse in the capital Tunis.
Police in the city of Sousse seized Jebali's phone and his wife's phone and took him to an unknown location, according to a statement by his family.
Nothing is certain in Tunisia's presidential election, only the second since the 'Arab Spring'.
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