Syria's opposition has accused President Bashar al-Assad's forces of gassing people with one report suggesting more than 1,300 people have died as a result of the alleged chemical attack.
Peggy Giakoumelos reports.
Syrian opposition groups allege more than 1300 people died in a massacre involving chemical weapons near the capital, Damascus.
A spokesman for the Syrian National Coalition, Khaled Saleh, is calling on UN chemical weapons inspectors - who have been in Syria since Tuesday - to do more to investigate the incident.
"What we want is from those inspectors to come in and see the people that were killed in the countryside of Damascus. We want them to look at the victims, we want them to investigate who used those chemical weapons. It's very obvious to us that these chemical weapons were used and were carried out using ballistic missiles. Only the regime has that capability and the willingness to use them against innocent civilians."
Videos distributed by activists - which have not yet been independently verified - appear to show medics attending children and adults struggling to breathe.
Others show rows of dead children and adults wrapped in white cloths, their bodies showing no obvious signs of injury.
But a spokesman for the Syrian military strongly denies the allegations relating to the use of chemical weapons.
"The media channels of sedition and misinformation who shed Syrian blood have lied as usual that the Syrian Arab Army used chemical weapons in the suburbs of Damascus today. The general leadership of the army confirms these allegations are completely false and are a part of the dirty media war that is led by some countries through the media against Syria."
The United States says it will consult with its partners on the United Nations Security Council about the reports.
White House spokesman Josh Earnest says US officials have not yet been able to independently verify reports about the use of such weapons in Syria by government forces, but he expressed alarm and called for an urgent United Nations investigation.
"I wouldn't want to speculate on what may or may not have happened. Fortunately, we have credible professional investigators with the United Nations on the ground in Syria right now, let us give them the opportunity to take a look at what happened, let us give them the opportunity to interview witnesses, let us give them the opportunity to collect some physical evidence, and then we we can reach a conclusion about what exactly happened there. But suffice it to say that though the use of chemical weapons is something that the United States finds totally deplorable and completely unacceptable, and those who are responsible for the use of chemical weapons, if it's determined that is what happened, will be held accountable."
The United Nations Security Council has held an emergency meeting to discuss the alleged chemical attack in Syria.
Security Council members France, Britain, the United States, Luxembourg and South Korea requested the meeting, which was held behind closed doors.
British Foreign Secretary William Hague is demanding UN chemical weapons inspectors get full access to the site of the alleged attack.
"If verified this would be a shocking escalation of the use of chemical weapons in Syria. We are determined the people responsible will one day be held to account. I hope it will be made clear that the UN team now in Damascus will have unrestricted access to the area concerned and the United Kingdom will be raising this at the United Nations Security Council."
The United Nations says more than 100,000 people have been killed since Syria's civil war erupted, pitting Bashar Al-Assad's government forces against opposition groups seeking to end his family's four-decade rule.
