Q&A: Syria 'toxic attacks' near Damascus

A youth, affected by what activists say is toxic gas, is treated at a hospital in the Duma neighbourhood of Damascus August 21, 2013

Many of the patients shown in the footage appear not to have outward injuries

Graphic footage shows what Syrian opposition activists say are the horrific results of chemical weapons attacks on the outskirts of Damascus.

The Syrian army has denied it used poisonous gas, calling the latest claims "false and completely baseless".

It has not been possible to independently verify the pictures - but here is what we know about the claims so far.

What happened?

What do the videos appear to show?

Many of the alleged victims were children

What do the apparent symptoms suggest?

What questions remain?

Could the video reports be fake?

Patients appeared to have severe breathing difficulties

Who would be capable of such an attack?

Why now?

How can the claims be verified?