The United States military says Syrian rebels they have trained have given vehicles and ammunition to the al-Qaeda-linked Nusra Front.Six pick-up trucks and about one-quarter of their issued equipment was handed over apparently in exchange for safe passage.The US has trained rebels to fight militants from the group calling itself Islamic State (ISIL).A statement issued by US Central Command (Centcom) said the report, if accurate, is concerning and a violation of Syria train-and-equip programme guidelines.Centcom overseas military operations in the Middle East. It was told of the equipment surrender on Friday evening, according to the statement. Earlier the same day, a Centcom spokesman had said all weapons issued to the rebels remained under their control.