Who uses chlorine in Syria?

The warring sides in Syria stand accused of attacking civilians with chlorine gas.

Video of a terrified young boy suffocating - and asking a medic if he was going to die - was shared on the internet a few days ago.

It's thought he inhaled chlorine gas in yet another barrel bomb attack on Aleppo.

Both government forces and opposition fighters are accused of dropping the bombs.

The attack highlights the continued use of chemical weapons, in contravention of an international ban.

But how are they obtained in Syria? And who's being held accountable for their indiscriminate use?