The specter of chemical weapons has been hanging over war-torn Syria for months.
Although viewed with skepticism by U.S. officials, the latest claims and counterclaims by the Syrian government and opposition forces over their alleged use in Aleppo province and a Damascus suburb have intensified concerns and prompted the United Nations to promise an investigation.
Syria's government insists it doesn't have chemical weapons, and wouldn't use them against its own people if it did, while the Syrian opposition says it neither has such munitions nor the means to make them.
Whatever the truth of the latest allegations, military analysts say they believe Syria may have one of the largest stockpiles of chemical weapons in the world. Specifically, the supply could include sarin and VX gases -- both nerve agents -- and mustard gas, which are banned under international law.
The prospect that these could potentially be deployed by an increasingly beleaguered regime has made many observers anxious -- and has been cited as a "red line" for robust action by the United States.
So why would Syria have such armaments?
Few munitions evoke as much fear as chemical weapons. And unlike nuclear weapons, they are relatively inexpensive to develop and stockpile.
This lends them a disproportionate importance for Syria and the region, analysts say.
"In the Middle East, chemical weapons have been seen as a possible counter to Israel's nuclear weapons," said Dr. Susan B. Martin, of the Department of War Studies at King's College London.
"They are seen as a possible strategic deterrent," she said, "and they are cheaper and easier to have than nuclear weapons."