The United Nations Security Council has called for a prompt and impartial investigation into claims of a chemical-weapon attack outside the Syrian capital, Damascus which is believed to have killed hundreds of people.
The Syrian Government and opposition fighters have both accused the other of being responsible.
UN officials say the alleged chemical weapons attacks were a "serious escalation".
The BBC reports that Deputy Secretary-General Jan Eliasson made the comments after briefing an emergency UN Security Council meeting about Wednesday's incident.
The Security Council also said that clarity was needed over the attacks.
Some 35 member states called for UN weapons inspectors already in Syria to be dispatched immediately to the scene.
Opposition activists said that more than 1,000 people were killed after government forces launched rockets with toxic agents into the Damascus suburbs in the Ghouta region early on Wednesday.
People who say they have been treating those caught in the attack have told the BBC the patients' symptoms included suffocation, foaming at the mouth and blurred vision.
Videos posted online showed pale lifeless bodies with no marks of exterior injuries and glazed expressions.
These cannot be independently verified, but experts say the symptoms are consistent with the use of the nerve agent, sarin.