Updated

The Air Force's top civilian and uniformed leaders said Wednesday the failure to prevent a teenager from stowing away aboard a military cargo plane, apparently while on an airfield in the African nation of Mali, was a serious security lapse.

The boy's body was found and removed from the plane at Ramstein Air Base in Germany on Sunday after it had returned from an eight-day mission to several African nations. Neither his identity nor his nationality has been disclosed.

"Whatever happened here, something fell through the cracks that this boy was able to gain access to the aircraft," Air Force Secretary Deborah Lee James said.

Air Force Chief of Staff Gen. Mark Welsh said the boy died of asphyxiation. His body was found in a compartment above the rear wheel well, and Welsh said an outside fuselage panel had to be removed to gain access to the body.

"How he got in there is a huge question mark," Welsh told a news conference where he and James were asked about the incident.

Welsh said he was told that the boy was believed to have stowed away while the C-130J cargo plane was on the ground in Mali. Northern Mali fell under control of ethnic Tuareg separatists and then al-Qaida-linked Islamic extremists following a military coup in 2012. A French-led intervention last year scattered the extremists.

Welsh said the incident is under investigation.

"It raised security flags for everybody involved," he said.

James said officials will review security protocols and what step were taken to protect the plane during the stop in Mali.

The C-130J cargo plane was being operated by U.S. Africa Command. Pentagon officials said it made stops in the African nations of Senegal, Chad and Tunisia, in addition to Mali, and stopped at a naval air station in Sicily before arriving in Germany.