The Pentagon admitted Friday that a group of U.S.-trained Syrian rebels surrendered arms and ammunition to an Al Qaeda affiliate in exchange for safe passage through the group's territory.

The rebels, members of New Syrian Forces militant group, handed over a total of six trucks packed with ammunition to Syrian jihadist group al-Nusra, according to Telesurtv.

"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, BBC News reported.

The admission came from Pentagon, which earlier denied al-Nusra's claims that rebels had handed over all of their weapons upon re-entering Syria, reported NBC News.

The U.S. Central Command, tasked with military operations in Middle East, announced an investigation into the matter.

The information "is very concerning and a violation of Syria train and equip program guidelines," Command's spokesman Col. Patrick Ryder said, according to The Los Angeles Times.

"In light of this new information, we wanted to ensure the public was informed as quickly as possible about the facts as we know them at this time. We are using all means at our disposal to look into what exactly happened and determine the appropriate response," Ryder said.