BRUSSELS – The United States has sent troops to Jordan to bolster its military capabilities in the event Syria’s civil war escalates, U.S. Defense Secretary Leon Panetta said Wednesday, reflecting U.S. concerns about the conflict spilling over allies’ borders and about the security of Syria’s chemical weapons arsenal.

Speaking at a NATO conference of defense ministers, Panetta said the U.S. has been working with Jordan to monitor chemical and biological weapons sites in Syria and also to help Jordan deal with refugees pouring over the border from Syria.

About 150 U.S. troops, largely Army special operations forces, are working out of a military center near Amman, two senior defense officials said on condition of anonymity because they were not authorized to speak publicly about the mission. The troops have moved back and forth to the Syrian border as part of their work, which is joint planning and intelligence gathering, one official said.