What is a barrel bomb? - Explained in 30 seconds
Syria's President Bashar al-Assad has denied in a BBC interview that his forces have used barrel bombs indiscriminately in civilian areas.
He insists that his air force has only targeted "terrorists" and that civilians have not been harmed.
But what are barrel bombs? And why is their use so controversial?
BBC News explains in 30 seconds.
Video produced by Mohamed Madi