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.

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.