US military officials admitted late Friday that a unit of Syrian rebels trained and equipped by the US-led coalition likely surrendered their supplies to al Nusra Front, al Qaeda's affiliate in the country.

The announcement came after US Central Command (CENTCOM) Wednesday assured journalists that "all Coalition-issued weapons and equipment are under the positive control of NSF," or the New Syrian Force, a paramilitary group sanctioned by the US-led coalition. That statement was issued in an effort to counter reports that NSF had handed over all their supplies to the al Qaeda affiliate upon entering Syria, and in response to a post on a Nusra Front-linked Twitter account that purported to show the group in possession of coalition equipment.

CENTCOM said it had earlier concluded that no supplies had been lost after conducting "an analysis of the image depicted in the Tweet and determined the claim to be false."

But whether the images posted on Twitter are real or not, officials Friday appeared to walk back their initial assessment, and reported that Nusra Front had in fact seized a sizable portion of its equipment.

"Today, the NSF unit contacted Coalition representatives and informed us that on Sept. 21-22 they gave six pick-up trucks and a portion of their ammunition to a suspected al Nusra Front intermediary, which equates to roughly 25 percent of their issued equipment," Col. Patrick Ryder, a spokesman for CENTCOM, said in a statement. "If accurate, the report of NSF members providing equipment to Al Nusra Front is very concerning and a violation of Syria train and equip program guidelines."

The acknowledgement is the latest blow to Washington's efforts to train a moderate rebel force to take on the so-called Islamic State and counter other extremist militants in Syria. The half billion dollar program that began a year ago has offered an embarrassing paucity of accomplishments. Earlier this month, CENTCOM commander General Lloyd Austin said there were only four or five fighters in the country, which is just 0.1 percent of what the Pentagon envisaged.

Other US-trained rebels have been attacked and partially surrendered to Nusra Front in the past, including a group that attempted to enter Syria in July.