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."