Syria’s opposition fighters have been supplied with U.S.-made, tube-launched, optically tracked, wire-guided (TOW) antitank missiles. This is the first time that a major American weapons system has appeared in Syrian rebel hands. It is unclear how the rebels obtained the wire-guided missiles, which are capable of penetrating any armored vehicle used by the Syrian army.
Source: The Washington Post
See also: US Secretly Sending Anti-Tank Weapons to Syrian Rebels