Western intelligence sources tell Fox News that Iran has started a clandestine air bridge from Tehran to Damascus to resupply Syrian President Bashar Assad with weapons, ammunition and men.

To get around international sanctions and airspace restrictions, the Iranians are using commercial airliners with unsuspecting passengers aboard. The planes fly seven times a week and include Iran Airlines flights. Passengers on-board have reported being held on-board flights for hours while the weapons are unloaded at Damascus airport.

Watch Leland Vittert's report below.