A car bomb exploded on Monday in a southern district of Damascus which is home to Syria's holiest Shi'ite Muslim shrine, according to the Syrian Observatory for Human Rights (SOHR).
The British-based monitoring group said the blast took place near a checkpoint used by the Syrian army and its allies.
Reuters reported that there was no immediate mention of the blast on Syrian state media, which normally reports bomb attacks in government-held areas, and Hezbollah's Al Manar TV denied any blast took place.
The area has been targeted several times by deadly bombings this year, most recently in June with an attack claimed by Islamic State.
The SOHR said initial reports indicated there were no civilian casualties on Monday.
The Sayeda Zeinab shrine is a magnet for thousands of Iraqi and Afghan Shi'ite militia recruits who go there before being sent to frontlines, where they fight against Sunni rebel groups trying to topple President Bashar al-Assad.
According to Shia Muslim tradition, the mosque contains the grave of Zaynab, the granddaughter of the Prophet Muhammad.
In September 2008, 17 people were killed when a car bomb exploded near the mosque.
In June 2012, 14 were heavily wounded during a suicide car bomb attack, also nearby.
The area has been under sustained attack from armed militants from neighbouring Sunni towns since the summer of 2012.
Shia and pro-government families have sought refuge in the Sayyidah Zaynab, the city of the same name as the shrine, having been driven out of their homes in southern Damascus.
A spokesman for the SOHR told Christian Today that it was not clear whether the mosque was specifically targeted in today's attack.
Additional reporting by Reuters.
