United Nations Secretary General Ban Ki Moon has called for the Syrian government to allow UN inspectors to investigate Wednesday's alleged chemical attack near the nation's capital.
The Syrian Opposition National Coalition claims that from 500 to well over one-thousand people were killed in what would be the world's most lethal chemical weapons attack since the 1980s.
International reactions to the claims have been varied, with most urging caution until the facts are laid out.
Horrifying images have been in circulation around the world since Wednesday, purporting to show victims of the alleged chemical weapons attack.
Footage distributed by activists appears to show unconscious children, people foaming around the mouth and doctors administering oxygen to help people breathe.
This child spoke about losing his family during a pre-dawn attack.
"We were sleeping downstairs and we heard a bang. It was very close. My grandfather came downstairs and rushed into the bathroom. He started vomiting, then convulsing. He died. My mother then fell and banged her head on the floor."
But the authenticity of the footage, or when or where it was taken, has not been verified.
And the Syrian government denies the use of any chemical weapons against rebel forces.
Rebel spokesman Louay Meqdad says that Syria's President Bashar al-Assad would stop at nothing to suppress the rebels.
"Today I think all the liberated areas are in real danger. North, south, and Homs province. All the liberated areas are in real danger because Bashar al-Assad today he has no red lines, he has nothing to lose. He wants to kill the revolutionaries whatever it takes, he wants to destroy the revolution whatever it takes."
The UN Secretary General Ban Ki Moon says the alleged use of chemical weapons should be investigated, and the Syrian government must co-operate with UN investigators already in the country.
"I'm especially troubled by reports that chemical weapons might have been used on the civilian populations. Any use of chemical weapons anywhere, by anybody, under any circumstances would violate international law. I have called on the Syrian government to extend its full co-operation so that the mission can swiftly investigate this most recent incident."
The 20 person UN team of investigators arrived last Sunday to investigate earlier reports of chemical weapon attacks.
But they have limited powers to investigate - with a mandate to visit just three sites previously agreed between the UN and the Syrian government.
Also their mission is only aimed at establishing whether chemical weapons have been used, not who used them.
Permission to inspect the area of the new alleged attacks has not been granted.
And the Syrian Information Minister Omram Al-Zoubi continues to deny any use of chemical weapons in the area.
"Everything that has been said is ridiculous, naive, unscientific, illogical and subjective. We mean what we are saying. There's not any use of that weapon at all. The military operation that's taking place on the ground is a successful one and our forces are making progress on all sides facing the armed groups."
International reactions to the alleged attack have been marked by widespread condemnation yet caution.
Prime Minister Kevin Rudd is among those calling for an investigation.
"We are now as an international community calling upon the Syrian government to give them full access to this most recent horrific incident in order to establish the facts. Establish the facts first then decide upon the appropriate and most effective form of robust international action."
The US has also struck a cautious tone.
US President Barack Obama warned last year that the use of chemical weapons in the Syrian conflict would cross what he called a red line, with the implied threat of intervention.
State Department spokesman Jen Psaki says if chemical weapons were used, the US doesn't believe it would be the rebel forces using them.
"We still believe that they don't have the capability to use chemical weapons. That has not changed. Again, we're looking into the facts on the ground, but there's no reason, if there's nothing to hide, for the regime not to let the investigative team in."
French Foreign Minister Laurent Fabius has vaguely called for a response of force from the international community if the use of chemical weapons is proven.
"If it is proven, for us, the position France is that there must be a reaction. What does that mean, a reaction? Not to send soldiers onto the terrain. But a reaction, of course, of international condemnation, but a reaction which could take the form - I don't want to be more precise - of force"
The UN says that more than 100,000 people have been killed in Syria's 29 month war and millions more have been forced to flee their homes.
