It was not immediately clear who was behind the overnight attack, and protesters said they did not know whether the masked gunmen were riot police, special forces or militias. Around 240 anti-government protester have been killed this month.
Officials say the attack took place in northern Sar-i-Pul province in which an Afghan Taliban commander was also killed. Separately, officials say Afghan forces freed at least 54 people from a Taliban prison in southern Helmand province.