At least 10 people were executed on Saturday in Syria's Aleppo city on the orders of a religious court dominated by al Qaeda affiliate al Nusra Front, the Syrian Observatory for Human Rights said.
The monitor said two of the executed were accused of adultery, with the rest accused of collaboration with the Syrian government.
The executions, in the eastern Aleppo neighbourhood of Shaar, were ordered by a religious court that includes several conservative rebel groups but is dominated by al Nusra Front.
All 10 men were shot dead, the Observatory said.
Islamic courts have been set up in many towns and villages in Syria that have been wrestled out of government forces' control by Islamist militants or jihadist groups.
Al Nusra has also carried out summary executions of government troops in areas captured by it.
More than 230,000 people have been killed in Syria since the conflict started in March 2011 with the inception of anti-government protests.