U.S. Defense Secretary Leon Panetta has signed an order to send two Patriot missile batteries and 400 troops to NATO-member Turkey.
Pentagon press secretary George Little said Panetta signed the order on December 14, shortly before arriving on an unannounced visit to Turkey to meet U.S. troops stationed at the Incirlik air base.
The deployment is part of a move by NATO members to bolster Turkey's defenses against the threat of Syrian missiles.
Germany and the Netherlands are also sending Patriot missile batteries to southern Turkey.
They will be placed under the command of NATO and are scheduled to be operational by the end of January.
Based on reporting by Reuters, AP, and the BBC