At least seven people were wounded, one of them in critical condition, during a protest that took place in Radfan district, Lahj province.
Protesters demonstrated in the town of Radfan against an army siege of a village in the southern province seeking to capture separatists.
Sources said security forces shot bullets at the protesters.
Last month, military reinforcements were deployed to the district after separatist militants stepped up attacks targeting troops and army posts as well as citizens and their properties, amid the continuous unrest in most o the south.