Syria is the first country with weapons of mass destruction (WMD) to be ripped apart by civil war. The United States and Britain have both warned Damascus not to use its chemical weapons. Here are five things to know about Syria's WMD.
What kind of WMD does Syria have?
Western arms experts say Syria has one of the world's largest chemical weapon arsenals.
Since Damascus began a WMD program with Soviet help in the 1980s, it has accumulated hundreds of tons of skin-blistering mustard gas and the fatal nerve agent sarin. It probably also has the nerve agent VX, which can linger in an area for weeks.
The agents are stockpiled but ready for battlefield use in artillery shells, aerial bombs, and Scud missile warheads.
It is not known whether Syria also has biological weapons. Leonard Spector, head of the Washington D.C. office of the Monterey Institute Center for Nonproliferation Studies, says "we know they have chemical weapons, including some of the most advanced, but the biological weapons issue is very unclear."
"The latest statement from the U.S. government is that they [Damascus] have done research in this but that they do not seem to have the ability to make actual biological weapons that could be delivered by bombs or by other means," Spector says.
Syria has made no progress toward nuclear weapons since a suspected reactor site was bombed by Israel in 2007.
Could Syria use WMD to crush the uprising?
That is nightmare scenario number one.
The precedent for doing so is right next door in Iraq, where Saddam Hussein dropped multiple chemical and nerve agents on the town of Halabja in 1988. The attack, which killed between 3,000 and 5,000 people, swiftly ended an Iraqi-Kurdish uprising at the time.
The Assad regime has warned it could use WMD to defend against "external aggression" but would never use them against fellow Syrians.
Dina Esfandiary at the London-based International Institute for Strategic Studies, says Damascus knows gassing its own people is not only a red line for the United States -- as President Barak Obama said this week -- but also for the Syrian government's own allies.
"Even Syria's allies, its very few friends, including Russia, have made it quite clear that use of chemical weapons would not be tolerated," Esfandiary says.
"So, even if Assad were immune to threats from the United States and Israel, surely when it is in its moment of need Russia's calls for it to be careful will resonate quite deeply."
Could Syria's WMD fall Into the hands of Al-Qaeda or Hizballah?
That is nightmare scenario number two.
Al-Qaeda has declared common cause with Syria's rebels and is operating in the country. That raises the danger that if one of the places where WMD is stored fell behind rebel lines, the international terrorist organization might have a chance to get them.
Spector notes that the stockpiles are guarded by elite troops "loyal to the regime and to their mission." But there is no certainty they would fight to the death if isolated. That leaves it to the West to find some means to assure that the Free Syrian Army would make it a priority to negotiate with any isolated site to assure it remains intact and out of Al-Qaeda's hands. Whether the Free Syrian Army has a sufficiently cohesive command structure to do that remains a question.
The other wild card in the Syrian struggle is the Lebanese Shi'ite Hizballah. The party's armed wing is supporting the Assad regime against the rebels in exchange for decades of support from Damascus in its fight against Israel. If the Assad regime crumbles, Hizballah might move to appropriate some of the WMD for itself.
Israel warned last month it is ready to intervene militarily if there is any indication that Hizballah is accessing chemical weapons in Syria.
But whether Hizballah will actually try to get WMD remains anybody's guess. Analyst Esfandiary expects Hizballah to refrain due to its own political goals.
"You have to keep in mind that Hizballah right now is trying to become a more legitimate actor, it is now a political actor in the Lebanese government, it is an actor which for the duration of its existence has criticized Israel's use of indiscriminate weapons, so how likely is it that they would accept chemical weapons? I think it would delegitimize them quite significantly," Esfandiary says.
Could the West bomb the stockpiles?
Arms experts say the locations of Syria's WMD are well known to U.S. and Israeli intelligence agencies, which monitor them constantly. The monitoring is sufficient to detect that Damascus moved some of its WMD last month, presumably to a safer location due to fighting.
But simply bombing stockpiles to remove the WMD threat is not a failsafe option. Spector notes.
"There are a couple of problems. One is you may not get everything. Two, you will destroy the bunkers, however, and some of the protective installations that are keeping these weapons relatively safe at the present time. You almost certainly would have offsite leakage of the gases," Spector says.
What about diplomatic solutions to the WMD threat?
That's what everyone hopes for. But the solutions mostly depend upon Damascus cooperating with Western and Arab demands for a peaceful transition of power in Syria.
U.S. Defense Secretary Leon Panetta last month called it important for Syrian security forces to hold together should Assad leave power. "They do a pretty good job of securing those sites," he noted in an interview with CNN. "If they suddenly walked away from that, it would be a disaster to have those chemical weapons fall into the wrong hands, hands of Hizballah or other extremists in that area."
But how the West might convince Assad to step down remains unknown. Those efforts were dealt a severe blow by the resignation this month of Kofi Annan as international peace envoy for Syria. His departure marked five months of fruitless diplomatic attempts to prevent the conflict in Syria from escalating further.