By Elise Labott

The United States and some European allies are using defense contractors to train Syrian rebels on how to secure chemical weapons stockpiles in Syria, a senior U.S. official and several senior diplomats told CNN Sunday.

The training, which is taking place in Jordan and Turkey, involves how to monitor and secure stockpiles and handle weapons sites and materials, according to the sources. Some of the contractors are on the ground in Syria working with the rebels to monitor some of the sites, according to one of the officials.

The nationality of the trainers was not disclosed, though the officials cautioned against assuming all are American.

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One of the aims, the sources said, is to try to get real time surveillance of the sites because the international community would not have time to prevent the use of the weapons otherwise. The program could explain how U.S. intelligence was able to learn what U.S. officials said was evidence the Assad government is mixing precursors for chemical weapons and loading those compounds into bombs. The intelligence, one U.S. official told CNN last week, came not just from satellite surveillance, but also from information provided by people. The official would not say whether the human intelligence came from telephone intercepts, defectors or people inside Syria.

The U.S. military is also working with neighboring Jordan's military to train for the potential need to secure chemical weapons sites. But U.S. troops cannot train rebel forces because the United States has only authorized nonlethal aid for the opposition.

Syrian President Bashar al-Assad seems to be backing off, at least for now, on the possible use of chemical weapons, after the major international outcry over the military activity, according to several sources. CNN reported Friday that the bombs are not being moved to any delivery devices and that the United States was not aware of any significant additional movement of chemical materials.

The Russians, who have allied with Syria, sent several strong messages to the Assad government over the past week against using chemical weapons, saying doing so would be a red line and Assad would lose Russia's support if he did. However, the sources said that the lull in activity could be short-lived and they believe that, if desperate enough, Assad would not hesitate to use such weapons.