US chemical weapons expert Dan Kaszeta says that from the evidence he has seen of the alleged attack in Syria, he would guess that a "toxic industrial chemical" had been used.
He stressed that it was impossible to tell in the absence of forensic evidence, but that the symptoms do not look like those caused by a nerve agent.
In this video, a young boy describes in Arabic how his family home was allegedly shelled and his relatives "smelt the gas" before showing a range of symptoms associated with a chemical attack.
The video was uploaded to a social networking website yesterday and does not give the boy's name or location. ITV News cannot independently verify it.
The video has been translated as follows: "Our granddad was at our house ... We were all asleep ... my grandad was upstairs and we were all downstairs ... The plane came and hit us ... and there was a huge sound ... We all woke up in shock ...
"My brother went upstairs to tell my grandad to come downstairs with the rifle ... As my brother was coming back downstairs he smelt the gas ... and he ran inside ... and then he just began to fit ... like he was going to die ...
"Then my mum and dad sat there and made him drink water ... and he kept throwing up ... After that ... he began to suffocate and he died ... My grandad then fell ... and was lying on the floor ... As my mum was trying to fan them ... she also fainted and was on the floor...
"[Interviewer: What did you do then?] I don't know ... I don't know how I got here ... I was crying and crying ... and then I was here ... My mum and dad are dead ... and my sisters and brothers ... [Interviewer: So who survived from your family?] Just me."
Syrian activists say President Bashar al-Assad's forces are pressing on with a military offensive in the rebel-held eastern Damascus suburbs, the Associated Press reports.
The Britain-based Syrian Observatory for Human Rights says it still cannot confirm the numbers of casualties in Thursday's bombing of eastern Ghouta, which the opposition alleges was a chemical attack.
A video journalist working in Syria says he is convinced there was a chemical attack in several suburbs of Damascus on Thursday.
Humam Husar spoke to Daybreak from the Syrian capital and said he believes the symptoms of the dying and injured leave no room for doubt.
The Iranian Foreign Minister Mohammad Javad Zarif said the Syrian government could not have been behind a possible chemical weapon attack on the outskirts of Damascus as President Bashar al-Assad's forces had the upper hand in the fighting.
If the use of chemical weapons is true, it has definitely been carried out by terrorist... groups, because they have proved in action that they refrain from no crime
The United Nations Security Council said it was necessary to clarify an alleged chemical weapons attack in the suburbs of Damascus but stopped short of explicitly demanding a probe by UN investigators in Syria.
Argentina's UN ambassador, Maria Cristina Perceval, told reporters after a closed-door emergency meeting of the council: "There is a strong concern among council members about the allegations and a general sense that there must be clarity on what happened and the situation must be followed closely."
The UN Security Council has agreed on a need for "clarity" in relation to the claims of a deadly chemical attack in Syria but has stopped short of calling collectively for a UN investigation.
Foreign Secretary William Hague has said he hopes the alleged chemical attack in Damascus "will wake up some who have supported the Assad regime to realise its murderous and barbaric nature".
Speaking ahead of tonight's UN security council meeting, Mr Hague said it was vital that the UN team in Damascus be given "immediate" and "unrestricted" access in the area of the alleged gas attack "to discover the truth".
"There is no reason for them not to be given access to a site not many miles (from) where they are (already) in Damascus," he said.