The Mayor of the Esenyurt district in Istanbul, Ahmet Özer, was arrested on Wednesday accused of alleged links to the banned and terrorist-stamped Kurdish PKK.
Hundreds of demonstrators gathered the same evening outside the courthouse in Istanbul where the formal charges were presented.
Özer belongs to the largest opposition party, the Republican People's Party (CHP), which says the arrest lacks grounds.
Together with the largest pro-Kurdish party DEM, which calls the arrest a "political coup", CHP is calling for new protests on Thursday.
