"All the stocks of these weapons that the Syrian Arab Republic possesses are monitored and guarded by the Syrian army. These weapons are meant to be used only and strictly in the event of external aggression against the Syrian Arab Republic," Makdissi said. He has since fled to the United States as a refugee, according to the U.S. envoy to Syria, Robert Ford.

In a letter to the U.N. secretary-general in December, Syria said the United States falsely accused it of using chemical weapons.

"What raises concerns ... is our serious fear that some of the countries backing terrorism and terrorists might provide the armed terrorist groups with chemical weapons and claim that it was the Syrian government that used the weapons," the state-run news agency SANA reported.

It was its formal request to the U.N. secretary-general that prompted the promise of an independent investigation into their alleged use.