A series of videos uploaded to YouTube by Syrian activists suggests rebels are beginning to focus on where Bashar al-Assad's regime stores its chemical weapons.
At the same time, a former senior officer in the Syrian Army who says he was chief of staff of chemical warfare has told CNN that Iranian technicians are helping with the regime's research into chemical weapons. He also said they could be easily transferred by the regime to Hezbollah, the Lebanese militia organization that fought a border conflict with Israel in 2006.
The videos were first uploaded in July. Narrators using Google Earth satellite imagery describe in detail several sites where they allege that chemical weapons and missiles are stored or manufactured.
There is no way for CNN to independently verify what the videos purport to show.
Adnan Sillu, a former major general in the Syrian Army, told CNN Friday that moving the weapons would be easy for the regime should they be at risk of falling into the rebels' hands.
"They are artillery shells and rockets that can be moved easily to Hezbollah," he added.
But Sillu denied remarks attributed to him that he had attended a meeting before he defected, during which the possible use of chemical weapons was discussed.
Sillu said he had heard that Syrian and Iranian experts were doing joint research at the long-established chemical weapons facility at Al Safir near Aleppo, where there is a complex of tunnels and a base for Scud missiles.
"There are warehouses there," he said, "used for experiments on poisonous grenades that contain sarin gas, tabun gas and mustard gas."
In a telephone interview from Turkey, Sillu told CNN that much of Syria's arsenal comprised poisonous gases.
"It's the weapon of choice for poor countries and Syria has large quantities of them. They sometimes takes the liquid form, and can be used in artillery shells or rockets," he said.
Of the several videos posted, the most detailed is about a military installation southwest of Damascus in al-Mazzeh, where a large military airport is situated.
An unnamed narrator says: "The chemical warehouse is connected with an underground tunnel that goes to the airport." The narrator identifies what appears to be the tunnel's exit. He says the tunnel is large enough to accommodate trailers.
There is no way for CNN to verify the descriptions given of the images, but the narrator claims considerable knowledge of the area. After zooming in, he points out a building described as housing equipment for ventilating the tunnel.
He says the warehouse is highly fortified with reinforced concrete that would be difficult to penetrate, even with cruise missiles. The area is called "Mezeh-86 and no-one can get in or out of it," he adds.
"The warehouse contains many chemical weapons, chemical bombs of different sizes, from the size of a hand grenade up to big rockets," he adds.
Sillu told CNN there was a chemical battalion headquarters in the area, but disputed there were warehouses of chemical weapons at the base.
The narrator also claims there are "experts from North Korea and Iran" housed in a building close by.
Again, it is impossible to confirm such claims, but Sillu said the head of the Syrian chemical warfare command had visited Iran and North Korea several times "to buy protective equipment against poisonous materials, and chemical equipment."
The possibility that the security of Syria's arsenal of chemical weapons and precursors might be compromised as fighting spreads is a source of deep concern to the Obama administration.
President Barack Obama himself said on August 20: "We have been very clear to the Assad regime -- but also to other players on the ground -- that a red line for us is we start seeing a whole bunch of chemical weapons moving around or being utilized."
"That would change my calculus; that would change my equation," the president said.
A U.S. official told CNN Friday the intelligence community believes it has a strong sense of where the weapons are and feels confident they remain under Syrian government control.
In another of the videos, a narrator identifying himself as Abou Sayyad uses Google Earth to illustrate an area between two settlements close to Damascus -- Al-Tal and Ish Al-Warwar. He describes the area as mountainous with poor roads. Zooming in, he points to an area that appears to show tunnels off a main road.
"This is a network of tunnels deep in the mountains that is secured against chemical and nuclear attacks where chemical and biological weapons are stored," he says.