She added: "The Syrian military has been very well trained in their use and deployment, so if anyone was to use them and use them successfully, it's Syria."
Modern armies are equipped to cope with such threats. Civilians, or ill-equipped rebel forces, are not.
If such weapons are fired in confined spaces, such as buildings, their effects are far more deadly than in the open air, said Lewis, of Chatham House.
An added danger is that chemical weapons have a long shelf life. Even if not usable as munitions, the chemicals can still present a threat decades on.
"One of the issues which is still being dealt with is munitions that are left over from the Second World War," said Martin.
How can you tell if chemical weapons have been used?
It's difficult to determine if chemical weapons have been deployed, unless you can recover a munition that still has traces of agent on it, said Martin.
Some conventional weapons or legal crowd control can also release smoke that causes respiratory problems, a common symptom of chemical weapons exposure.
This seems to have been the case in Homs last December, where the Syrian government was accused of using chemical weapons against civilians.
A U.S. State Department investigation subsequently concluded that the Syrian army did not use chemical munitions but apparently misused a riot-control gas in the attack, which Syrian doctors and activists said killed six people and left dozens suffering from respiratory, nerve and gastrointestinal ailments.
In order to be sure of what happened, it's key to get people on the ground quickly who can speak to any alleged attack victims, study medical records and analyze samples before they decompose, said Lewis.
The United Nations investigation team will be sent to Syria "as soon as practically possible," U.N. Secretary-General Ban Ki-moon said, but it's a complex mission that will not happen overnight.
U.S. officials remain to be convinced that the claims of chemical weapons use either in Khan al-Asal or in the rural Damascus suburb of Ateibeh are credible.
U.S. President Barack Obama and other American officials have said they are "deeply skeptical" of Syrian government claims that the opposition used chemical weapons.
Analysts are also "leaning hard away" from the notion that Syria used chemical weapons against its own people, a U.S. military official directly familiar with the preliminary analysis told CNN.
Pictures of the supposed victims of the chemical weapons attacks do not show the signs of burns or other symptoms that one might expect to see as a result of sarin, mustard gas or VX use, Esfandiary said.
What's to stop Syria from using its reputed arsenal?
The use of chemical weapons could be the final straw that pushes the international community to intervene directly in the two-year-long conflict.
After the latest claims, Obama reiterated his warning to Syria's government that it would be held accountable for the use of chemical weapons "or their transfer to terrorists."
He first warned last August that any sign of chemical weapons being moved around in large quantities or utilized would be "a red line for us."