Syrian authorities have arrested a pro-government activist who launched a social media campaign calling on officials to provide information about hundreds of missing soldiers, residents and activists said Monday.

The arrest on Friday has fueled an already unusually bold push by some government supporters to hold officials accountable for the rising death toll among President Bashar Assad's loyalists.

Before his disappearance, activist and lawyer Mudar Hassan Khadur represented a rare but growing voice of public dissent among Alawites, an offshoot sect of Shiite Islam to which Assad and many of his top military and security advisers belong.