Damascus is the chemical weapons capital of Syria, with vast and often secret research, production and storage facilities littered across the city. Click around this interactive guide.
(Click on the numbers below to explore the chemical facilities in Damascus. The interactive graphic will not work in Internet Explorer 8)
As Barack Obama joins western leaders in Britain and France in saying there is "conclusive" evidence of chemical weapons use by Bashar al-Assad's government, a street by street war is being waged in the streets of Syria's capital city.
That battle, according to claims by Syrian rebels, also features chemical weapon attacks. Within a couple of miles of these battles are facilities such as Jomarayah (3) where chemical weapons are researched and developed.
Research by Channel 4 News has revealed the network of jealously protected weapons facilities dotted across Damascus, and the claims by both the rebels and government of chemical weapons use. Rebels have made allegations of at least 30 different chemical weapons attacks by the government; the government has made one.
The research includes monitoring and translating thousands of videos and social media updates from rebels groups and the government alike.
One of the key facilities is Jomrayah - nestled in the mountains above the city. Jomrayah has been the target of missile attacks by Israel amid fears long-range missiles were being handed over to Lebanese militant group Hezbollah.
The Jomrayah facility includes a centre for hosting Iranian military experts, linked to Hezbollah.
It is also close to one of Damascus's frontlines. Syrian rebels who captured the town of al-Zabadani to the north west of the city have progressed down a valley in the mountain, and are now fighting President Assad's army for control of Qudssaya, the town next to the facility.
In the south west of the city, the areas of al-Moadamyeh and Darayya have been decimated by battles between rebels and government soldiers. Here the target is the Mazeh military airport - which is itself linked to a nuclear facility (2).
Mazeh features a secret bunker, deep underground and with extremely thick walls, where chemical weapons are stored. It is connected to the military airport by an underground tunnel.
Near the site, a compound called home by Maher al-Assad, the Syrian president's brother and a commander in the Republican Guard. And it is not just home for the president's family - there is also a residence for North Korean and Iranian military experts.
The frontlines in Damascus, as can be seen on the map above, have seen the Syrian government pushed back agains the Qasioun mountain, though they have also retained other important industrial and military areas around the city.
These mountains are heavily fortified with Syrian government forces - and also contain miles and miles of missile sites, chemical weapons storage and underground bunkers.
Syrian rebels swept across vast areas of Damascus from the east, aided by the fact that the fertile and flat region to the east of the city provides wooded cover. The battle now is in the built-up parts of the city - slowing the rebels' advance as they have to battle for the capture of each street.
The closest the rebels have comes to the heart of the city - the place where the organs of power are located - is in Jobar. And it is here where many of the alleged chemical weapons attacks against rebels have taken place.
One video, from 7 April 2013 (see below), allegedly shows the victims of chemical weapons warfare displaying symptoms such as foaming at the mouth, and pinpoint pupils.
Other videos, purporting to be from the same day, show clouds of what is alleged to be smoke from chemical bombs floating over Jobar. Videos posted online also show victims and smoke from alleged attacks in Jobar on 14 April and 5 May 2013.
Rebel claims about the use of chemical weapons in Damascus spread all over the city. The town of Otaybah, a rebel stronghold which is near to Damascus international airport, a rebel target, is one such place where claims have been made (see video, below).
Another video (below), posted by the jihadi al-Islam brigade, shows victims in Adra, to the north east of Damascus. The area around Adra is also home to vast chemical weapons storage facilities and missile bases (5). It is controlled by government forces.
This attack in Adra is one of four which the US has highlighted in its belief that the government has used chemical weapons. The other three are an attack in the Aleppo neighbourhood of Sheikh Maksud, the Aleppo suburb of Khan al-Assal, and the town of Qasr Abu Samra, to the north of Homs.
Research: Kamal Kaddourah, David Doyle
Graphic: Ciaran Hughes
Interactive will not work in Internet Explorer 8
14 June 2013