Two Mexican soldiers face military charges after a video surfaced of them helping a federal police officer torture a female suspect, the army said Thursday.

A female military police officer is seen in the video interrogating the woman. She pulls the woman's hair and puts the muzzle of a rifle against her head. Later, a blue-uniformed federal police officer puts the woman's head inside a plastic bag until she almost passes out.

The Defense Department said the events occurred Feb. 4, 2015, in Ajuchitan, a small mountain town in southern Guerrero state. Opium poppy plantations are common in the area, where drug cartels operate.

The National Security Commission, which oversees federal police, said its internal affairs unit had launched an investigation, and the Attorney General's Office said it has been investigating the events since January.

Mexico's army said the two soldiers were in a military prison facing charges of failure to obey orders.

Under Mexican law, civilian prosecutors are supposed to investigate army abuses against civilians, but soldiers can also face simultaneous charges in military tribunals.

The four-minute video, which was apparently made by a police officer or soldier, shows the handcuffed woman sitting in the dirt, crying, outside a rural cinder-block house.

The female soldier asks repeatedly during and after the torture: "Are you going to talk? Yes or no? Now do you remember?"

As the suspect lies inert on the ground, the female soldier asks: "Do you remember now? Or do you want the bag again? Or water? Or (electric) shocks? Tell me what you want."

The military justice system acted much more quickly in the case than civilian prosecutors. The army said it found out about the video in December and arrested the two soldiers in January. Civilian prosecutors could not say whether any charges had been filed against anyone in civilian courts.

Raul Benitez, a security specialist who teaches political science at the National Autonomous University of Mexico, said, "The military justice system tends to be very strict in such cases, because (the soldiers in the video) are casting the institution in a bad light."

Benitez noted the case is unusual in that the proof is so obvious and unarguable.

"There are abuses by soldiers, but there often isn't this kind of solid proof," he said. "They are not accustomed to acknowledging such cases, unless the evidence is overwhelming."

The Americas director for Human Rights Watch, Jose Miguel Vivanco, said that "torture and inhuman, cruel and degrading treatment continue to be the traditional methods of 'investigation' and punishment in Mexico."

"As long as those directly responsible for these practices, and those who cover up for them, aren't brought to justice, there will never be any chance to combat or eliminate" torture, Vivanco said.

The army said that "ïn this case or any other case where military personnel abuse human rights, energetic and rigorous action will be taken against those responsible."