The rebel held positions on the outskirts of Damascus that came under alleged government nerve gas attack on Wednesday are facing fresh bombardment from Assad artillery.
Syrian activists claim the number of dead in the toxic attack has passed the thousand mark.
The UN says it is necessary to clarify the alleged use of chemical weapons, but resisted calls to order a probe by inspectors already in Syria.
As many as 35 countries have called for an urgent UN investigation into the atrocity.
Maria Cristina Perceval president of the UN security council made the following statement:
“All council members agree that any use of chemical weapons by any side, under any circumstances, is a violation of international law.”
All eyes now turn to Ake Sellstrom and his team in Damascus.
The US says the delegation is prepared to investigate the allegations and said such an action is “consistent with its purpose and mandate.”
Turkey contacted the UN to say it was clear toxic material was used and demanded an inquiry.