More than a dozen villagers have been gunned down in a botched security operation in northeastern India, on the border with Myanmar. The incident has sparked violent clashes between locals and law enforcement agents.

Tensions have been running high in the Mon district of India’s northeastern Nagaland state after security forces conducted an “anti-insurgency” raid in the area, mistaking civilians for armed militia.

Nagaland में भारी बवाल, फायरिंग में 13 लोगों की मौत से भड़के ग्रामीण, सुरक्षाबलों की गाड़ियां फूंकी – आज तक

The Indian Army said the operation it undertook late on Saturday had been carried out “based on credible intelligence.” It had reportedly been tipped off about the movements of members of the separatist group the National Socialist Council of Nagaland in the Tiru area, but the officers ended up mistaking a pickup truck transporting civilians for the insurgents and opened fire on it.

“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,” the military said.

Local media reported that 13 civilians had been killed in the ambush-style operation on Saturday night, all of them coal miners returning to their village. The police later confirmed that number. At least 11 other people were said to have been injured in the shooting, and two others are still missing.

When the locals found out about the incident, an angry mob surrounded the security forces, blaming them for killing innocent people. Things swiftly got out of hand, with clashes breaking out and the troops firing at the crowd.

The police said that at least seven protesters had been injured as the soldiers acted in “self-defense.” One serviceman was killed and several others wounded, and three SUVs used by the security forces were set on fire, according to the military.

Indian Home Affairs Minister Amit Shah said he was “anguished” by the botched security operation, and promised the authorities would “thoroughly probe this incident to ensure justice to the bereaved families.”