Three members of a family were among five people shot dead by suspected United Liberation Front of Assam-Independent men while two others were injured at Kheroni in Assam's Tinsukia district on Thursday night, police said.
A group of assailants with sophisticated weapons came to Kheronibari village near Dhola-Sadiya bridge and called out five-six people from their house around 8 pm, they said.
They then opened indiscriminate fire upon those people before fleeing under the cover of darkness, a police officer said.
Police suspect the gunmen belonged to the ULFA-Independent faction as they were in battle fatigue.
Chief Minister Sarbananda Sonowal condemned "the killing of innocent people" and conveyed his sympathy to the bereaved families.
"Strong action will be taken against the perpetrators of this dastardly violence. We will not tolerate such cowardly act," he said.
Sonowal said he has directed state ministers Keshav Mahanta and Tapan Gogoi along with DGP Kuladhar Saikia to rush to the spot.
"We will not spare the culprits of the killings and they will be brought to book," he said.
The chief minister appealed to the people of Assam to maintain peace and harmony.
He also directed all deputy commissioners and SPs to remain alert.
Home Minister Rajnath Singh expressed deep anguish over the killings, saying strongest possible action will be taken against the perpetrators of the heinous crime.
Singh also spoke to Sonowal and took stock of the situation.
"Deeply anguished by civilian casualties in an attack in Upper Assam region. It is a reprehensible act of mindless violence. Spoke to Assam CM Shri @sarbanandsonwal regarding the incident and asked him to take strict possible action against the perpetrators of this heinous crime," he said.
According to Tinsukia Superintendent of Police Mukdhajyoti Mahanta, the bodies have been taken to the Sadia Civil Hospital for postmortem.
Industries and Commerce Minister Chandra Mohan Patowary, former chief minster Tarun Gogoi, opposition Congress state president Ripun Bora, All India United Democratic Front general secretary Aminul Islam and the Assam Sahitya Sabha were among those who also denounced the incident.
Meanwhile, West Bengal Chief Minister Mamata Banerjee, in a Twitter post, wondered if the attack was related to developments around the National Register of Citizens.
"Is this the outcome of recent NRC development," she questioned.
Banerjee strongly condemned the incident and offered condolences to the families of the deceased.
"Terrible news coming out of Assam. We strongly condemn the brutal attack in Tinsukia... We have no words to express our deep sorrow to the grieving families. The perpetrators must be punished at the very earliest," she added.