The specific sites of the alleged chemical attack are far from clear but reports by activists suggest they are concentrated in a cluster of rebel-held suburbs to the east of Damascus.
These built-up areas - known collectively as Ghouta - have seen intense fighting between the Syrian Army and rebel groups in the days leading up to Wednesday's alleged attack.
Rebels have been able to make large gains in the east of the capital largely because of the cover afforded by patches of woodland.
Other alleged sites of attacks tend to be around key military installations, such as chemical weapon stores near the town of Adra.
Jobar and Zamalka
These neighbourhoods to the north-east of city were allegedly the focus of Wednesday's chemical attack.
Jobar is the closest the rebels have come to the heart of the capital and is around two miles from the walls of the historic city - the seat of government power.
Both areas have reportedly seen scattered fighting in the streets.
Jobar also contains an ancient synagogue and is a pilgrimage destination for Syrian Jews, who have faced discrimination here.
Zamalka has a population of some 44,661 people according to the 2004 census, but there is no data on Jobar.
Irbin, Hammouriya, Saqba and Kfar Batna
The Syrian Army has been making efforts to regain control of this ring of small suburbs on the north-eastern edge of Damascus, which border Jobar and Zamalka.
They are all the sites of alleged chemical attacks, with one activist group claiming to have found more than 350 bodies here since Wednesday.
On Tuesday, activists reported that more than 60 mortar shells struck Kfar Batna, killing at least 11 people.
A large suburb north-east of the city that has seen large anti-government demonstrations and intense fighting between rebel groups and the Syrian army. Control of the area has passed back and forth between these two armies.
Activists say they have found 61 bodies here, but Amnesty International researcher Cilina Nasser tells ITV News she believes that victims were brought here from other areas that came under attack.
It had a population of some 317,679 people as of December 2009.
Rebels have also claimed the use of chemical weapons in the town of Otaybah, a rebel stronghold several miles to the east of the capital.
Videos on social media sites also claim to show victims of chemical weapons in Adra, a town several miles north-west of Damascus.
The town is adjacent to a large industrial facility and is, according to Channel 4 News, close to "vast chemical weapons storage facilities and missile bases".
Channel 4 reports that the US has highlighted Adra as one of four likely sites of a chemical attack.
Al Mouadamiya and Darayya
These areas to the south-west of city have been decimated by battles between rebel groups and the Syrian army, according to research by Channel 4 News.
The target is reported to be the Mazeh military airport - which is linked to a nuclear facility where chemical weapons are also stored.