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The Syrian government has revealed three previously unknown chemical weapons facilities to an international watchdog group, Reuters reported on Wednesday.

Damascus told the Organization for the Prohibition of Chemical Weapons (OPCW) at least one of the plants had been used to make ricin, according to Reuters. Another facility was used to experiment with various forms of chemical weapons.

The revelation is an indication that Syria violated a U.S.-Russian agreement calling on Damascus to provide a complete list of all its chemical weapons after a sarin gas attack killed hundreds of people in the town of Ghouta last summer. Damascus agreed to similar terms under the 1997 Chemical Weapons Convention, promising to halt the development, storage or use of any chemical weapons under the OPCW's supervision.

"Syria will argue that the facilities were not revealed earlier because they were in a rush when they first had to report them," one source explained to Reuters. "They had said the ricin was for medical purposes, but we don't believe that's true."

Pressure on Assad to be forthright about the existence and whereabouts of weapons has only increased since the Islamic State has claimed large areas of Syria, stoking fears that the extremists might gain hold of chemical weapons.

Just last week the OPCW debunked Syria's denial of targeting northern villages with chlorine gas, saying the country "systematically and repeatedly" deployed the weapon. 

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