Soldiers opened fire on a truck they believed was carrying militants in India's Nagaland state, and then shot locals who came to protest the killings.

More than a dozen civilians were killed by Indian security forces in the northeastern state of Nagaland, government officials said Sunday.

The civilians, who lived in a remote village along the border with Myanmar, were mistakenly believed to be militants.

Home Minister Amit Shah said he was "anguished" by the killing in Nagaland's Oting village.

"I express my deepest condolences to the families of those who have lost their lives," he said, adding that an investigative team set up by the state would "thoroughly" probe the incident.

The top elected official of Nagaland state, Neiphiu Rio, offered his condolences to the victims' families on Twitter, saying the killings were "highly condemnable."

The unfortunate incident leading to killing of civilians at Oting, Mon is highly condemnable.Condolences to the bereaved families & speedy recovery of those injured. High level SIT will investigate & justice delivered as per the law of the land.Appeal for peace from all sections

— Neiphiu Rio (@Neiphiu_Rio) December 5, 2021

What happened?

The victims were daily wage laborers who were returning home from a coal mine on Saturday evening in a pick-up truck when they suddenly came under fire.

They were ambushed by the army's para commando unit that was taking part in a counterinsurgency operation.

The soldiers fired at the truck after receiving intelligence about a movement of insurgents in the area, an unnamed army officer told the Associated Press. Six people in the truck were killed.

Villagers angered over the killings set fire to two army vehicles in protest. The soldiers responded by firing at them, killing seven more people, the army officer said.

What did the army say?

The army said in a statement that the unit was acting on the basis of credible intelligence of likely movement of insurgents.

"The incident and its aftermath are deeply regretted," the army said in a statement.

"The cause of the unfortunate loss of lives is being investigated at the highest level and appropriate action will be taken as per the course of law."

Indian security forces have been battling dozens of ethnic insurgent groups in the country's northeast, whose demands range from independent homelands to maximum autonomy within India.