A team of United Nations inspectors has reached rebel-held territory outside Damascus as UN Secretary-General Ban Ki-moon cautioned against pre-empting the chemicals investigation.
Activists confirmed the inspectors had reached the town of Maleiha and were being escorted to towns where deadly gas strikes are alleged to have happened.
Ban's message came as leaders in the west plotted taking military action against the Assad regime over the alleged attacks.
"It is essential to establish the facts," he said from the Hague. "A UN investigation team is now on the ground to do just that. Just days after the attack, they have collected valuable samples and interviewed victims and witnesses. The team needs time to do its job."
UN experts have begun the second day of their inspection of the site of an alleged chemical attack near Damascus, witnesses have told Reuters.
Humanitarian group Medecins Sans Frontieres has said there are strong indications that a chemical attack was carried out in Syria. It added that doctors had treated thousands of people suffering from neurotoxic symptoms.
The Assad regime has tried to shift the blame for the attack today on rebels whilst still refusing to allow the UN to investigate.
French medical charity Medecins Sans Frontieres (MSF) has said they were certain a neurotoxic agent was used in Syria after an alleged chemical attack in a suburb of Damascus.
MSF France President Mego Terzian said he was "almost certain" a neurotoxic agent had been used on the victims but could not say who was responsible for the attacks.
Medecins Sans Frontieres says there is strong evidence that the “large number of patients” doctors have treated in Syria were exposed to a “neurotoxic agent”.
Medical staff working in these facilities provided detailed information to MSF doctors regarding large numbers of patients arriving with symptoms including convulsions, excess saliva, pinpoint pupils, blurred vision and respiratory distress.
The reported symptoms of the patients... strongly indicate mass exposure to a neurotoxic agent. This would constitute a violation of international humanitarian law, which absolutely prohibits the use of chemical and biological weapons.
Medecins Sans Frontieres says doctors have treated about 3,600 patients with 'neurotoxic symptoms' in Syria and that 355 of them died.
Neurotoxicity hits people who are exposed to toxic substances and suffer problems to their nervous system as a result.
Syrian state television is reporting that government soldiers found chemical agents in rebel tunnels in the Damascus suburbs of Jobar this morning. The government run station quoted a "news source" as saying:
In some cases, soldiers are suffocating while entering Jobar. Ambulances came to rescue the people who were suffocating in Jobar.
Activists say more than a thousand people were killed in a chemical attack in Jobar on Wednesday morning.
Britain has directly accused the Assad regime of gassing hundreds of Syrian civilians amid warnings only 48 hours remain to find proof.Read the full story ›
A Syrian filmmaker has said hospital workers in Damascus are struggling to identify babies who survived the alleged chemical attack because their parents may already be dead and buried.
Speaking on Skype, Humam Husari told ITV News a large number of bodies were buried before they had been identified.
World leaders are facing diplomatic deadlock over Syria, caught between video evidence that strongly suggests a chemical attack, and the absence of concrete evidence.
Footage obtained by ITV News shows the aftermath of the alleged attack: Men, women and children lying dead where they fell.
Whatever killed them will have dispersed quickly, meaning that their bodies are likely to be the only evidence about its nature.
ITV News correspondent Paul Davies reports: