BEIRUT – The U.S. and regional allies are closely monitoring Syria's chemical weapons – caught in the midst of a raging civil war – but options for securing the toxic agents stuffed into shells, bombs and missiles are fraught with risk.

President Bashar Assad's embattled regime is believed to have one of the largest chemical weapons stockpiles in the world. Fears have risen that a cornered Assad might use them or that they could fall into the hands of extremists, whether the Lebanese Hezbollah militia, an Assad ally, or al-Qaida-inspired militants among the rebels.

For now, the main storage and production sites are considered secure. However, some suggest the civil war poses one of the gravest risks of losing control over non-conventional weapons since the breakup of the Soviet Union two decades ago.