There is new evidence of chemical attacks being carried out in Syria.

Government forces are thought to be behind many of them, but forces from the group calling itself Islamic State are also said to have used the weapons.

The BBC has seen evidence of the use of both mustard gas and chlorine, despite a commitment by President Bashar al-Assad in 2013 to dismantle Syria's chemical weapons stockpile.

Medical workers in some of the most troubled areas say many civilians are being targeted in what international law would categorise as a war crime.

Ian Pannell reports.