"For the first time in the history of the Chemical Weapons Convention (CWC), which entered into force in April 1997, there are serious concerns that chemical weapons might be used," said Ahmet Uzumcu, director-general of the Organisation for the Prohibition of Chemical Weapons.

U.S. President Barack Obama warned Syria that any deployment of chemical agents would be catastrophic.

"The use of chemical weapons is and would be totally unacceptable," Obama said this week. "And if you make the tragic mistake of using these weapons, there will be consequences, and you will be held accountable."