ISR comment: How the U.S., directly and indirectly, ended up arming al-Qaeda and its derivatives? These groups were armed directly by Saudi Arabia and Qatar, as part of the training and equipping of the so-called "Free Syrian Army", they also took U.S. hardware when they overran northern Iraq, and continue to receive arms through groups still trained and equipped by U.S. and its Gulf States allies.
A group of US-trained Syrian rebels has handed over their vehicles and ammunition to fighters linked to al-Qaeda, the US military has admitted.
It said one rebel unit had surrendered six pick-up trucks and ammunition to the al-Nusra Front this week - apparently to gain safe passage.
Congress has approved $500m (£323m) to train and equip about 5,000 rebels to fight against Islamic State militants.
But the first 54 graduates were routed by al-Nusra Front, the military said.
Gen Lloyd Austin told US lawmakers last week that only "four or five" US-trained rebels were still fighting.
"Unfortunately, we learned late today that the NSF (New Syrian Forces) unit now says it did in fact provide six pick-up trucks and a portion of their ammunition to a suspected al-Nusra Front (group)," Pentagon spokesman Cpt Jeff Davis said on Friday.
Meanwhile, Col Patrick Ryder, a spokesman for US Central Command (Centcom), said this happened on 21-22 September.