“Syria’s opposition fighters have been supplied with U.S.-made antitank missiles, the first time a major American weapons system has appeared in rebel hands. It is unclear how the rebels obtained the wire-guided missiles, which are capable of penetrating heavy armor and fortifications and are standard in the U.S. military arsenal. The United States has sold them in the past to Turkey, among other countries, and the Pentagon approved the sale of 15,000 of the weapons to Saudi Arabia in December. Both countries aid Syrian opposition groups. U.S. officials declined to discuss the origin of the weapons but did not dispute that the rebels have them…………”

You have two and a half guesses as to the source of these anti-Tank missiles (TOWs) in Syria. The two full guesses would be about the indirect sources; that would be Saudi Arabia and Turkey. Either one is a very likely the source, or both, although the U.S. arms deals stipulate against the resale to third parties. As to the ‘half source’, that would be the country of manufacture, either directly or, more likely, indirectly on a limited restricted trial-balloon basis.
Still, it is not as bad as supplying anti-aircraft missiles. If that happens, you can only imagine the nightmare scenario for airliners along the eastern Mediterranean.