Dozens of people were killed at dawn in Douma city to the northeast of the capital Damascus, with both the government and the rebels accusing each other of the massacre.
The state-run SANA News Agency said that an "armed terrorist group has committed an ugly massacre that claimed the lives of 25 people who were killed by knives near Hawa Mosquein Sli Bin Taleb Street in Douma."
The opposition accused the Syrian government of being behind the “massacre".
More top news
Merrill Lynch has been fined £34.5 million for failing to report 68.5 million transactions, the Financial Conduct Authority has said.
Most people back a change in the law to ban unpaid internships that last for more than four weeks, a new poll suggests.
The favourites to win the Venice marathon finished behind a local runner - after they were led along the wrong route by a motorcycle guide.