Acitivists say a car bomb has exploded outside a mosque in southern Syria, killing at least 22 people.

The Britain-based Syrian Observatory for Human Rights says the blast took place around the time of Friday prayers in the opposition-held town of Namar in Daraa province.

Observatory director Rami Abdurrahman says at least 30 people were wounded.

Abdurrahman says it is not clear who was behind the bombing.