Southern Movement opposition chief leader Hassan Baoum was arrested Sunday in Aden by Yemeni authorities from Nakeeb hospital.
Sources added that he was taken to the hospital Saturday night after having a heart attack.
Authorities accused Baoum of inciting and calling for separating the south from the north.
Lately, Hassan Baoum called for the Day of Rage to be held in southern provinces against Yemeni government.