The United Nations is now saying it has no conclusive evidence of chemical weapons use in Syria.
The statement marks an about-turn from statements made by Investigator Carla Del Ponte at the weekend when she suggested that rebels had been using the banned nerve agent sarin.
The Syrian government has renewed its demand for an investigation on the ground in Syria, and has called for it to take place as soon as possible.
"We are a hundred percent confident that Syria did not use chemical weapons against its own people. We are one hundred percent sure, but the opposition are fabricating all of these lies to create a real problem and to cover up for the crime committed in Aleppo. Through you we tell the United Nations to come immediately," said Syria's Deputy Foreign Minister Faisal Mekdad.
In America, President Obama has said a red line will be crossed if chemical weapons are used, and some appear convinced they already have - by the government.
"We find it highly likely that chemical weapons, if they were in fact used in Syria - and there is certainly evidence that they were - that the Assad regime was responsible," said White House spokesman Jay Carney.
In a separate development in Washington the chairman of Congress's Foreign Relations Committee, Senator Robert Menendez, has introduced a bill which, if passed by house, senate and president, would provide weapons for selected rebel groups.