An army officer and seven soldiers were detained in connection with the killing of 22 people in rural southern Mexico, authorities announced late Thursday.

The Mexican Defense Department said in a statement that the eight were involved in the incident in San Pedro Limon. They were being held at a prison in Mexico City on charges of crimes against military discipline, disobedience and breach of duty.

The statement said the military charges are "independent of the investigations that civil authorities are carrying out."

Recent reforms require that military offenses against civilians be tried in civilian courts, but nothing appears to bar the military justice system from pursuing parallel charges for breaches of military discipline,

Shortly after the June 30 confrontation, the army reported that 22 suspected criminals had been killed in a firefight. But just one soldier died, raising suspicions.

When The Associated Press visited the scene soon after the killings, there was no sign of a prolonged battle. Physical evidence suggested at least some of those who died had been shot at around chest level as they were standing against a wall.

Last week, a woman who says she witnessed the events said only one person died in the initial confrontation. She said the other 21 were killed after surrendering to soldiers.