A vicious Mexican drug gang forced some members to eat the hearts of murder victims as part of a gruesome initiation rite to root out infiltrators, a government security official said on Tuesday, citing witness testimony.

For much of the past year, Michoacan, a mountainous, agricultural state in western Mexico, has been ravaged by fighting between drug gang henchmen and vigilantes who took up arms against the cartels but have since splintered into violent factions.

A mid-December shootout between two rival groups that killed 11 people has reignited fears the government is failing to control the state after flooding it with federal troops and pressing vigilantes into a fledgling rural police force. Interviewed on local television, Alfredo Castillo, Michoacan’s federal security commissioner, denied cannibalism was widespread, but said there were various testimonies indicating heart-eating was part of a macabre initiation Moreno used to root out moles or test his men’s loyalty.