Assam police Friday launched a "massive combing operation" to arrest those involved in the killing of five people, including three members of a family, in Tinsukia district.
Police suspect the gunmen belonged to the ULFA (Independent) faction as they were dressed in battle fatigue, but the outfit has denied its involvement in the attack.
A group of assailants had called out six people at Kheronibari village - three from their home and as many from a local shop - around 8pm on Thursday.
They then took them to the edge of Dhola-Sadiya bridge in the area and opened indiscriminate fire, killing five of them on spot.
One of them fell off the bridge and survived the firing.
Director General of Police Kuladhar Saikia and Additional DGP Mukesh rushed to Tinsukia, shortly after the incident, to review the law and order situation.
Talking to media in Guwahati, Mr Saikia said, "A massive combing operation has been launched to nab the accused. No one involved in the incident will be allowed to escape. Since last night (Thursday), we have started several operations to nab the culprits."
Asked about the involvement of ULFA factions in the killings, he said, "It isn't about taking random names. We will take action as per law."
The lone survivor in the incident, identified as Sahadeb Namasudra, told reporters Friday morning he had a "providential escape" as he fell off the edge of the bridge, where the gunmen had lined up the six persons and shot five of them dead.
Though he did not sustain injuries, he fell unconscious out of fear and nervousness.
On regaining consciousness, he found one of the five persons still alive beside him, Namasudra claimed, adding that the man died before any arrangement for help could be made.
Publicity Department member of the ULFA(I) Romel Asom, in a statement e-mailed to PTI here, said, "The ULFA (I) would like to make it clear to all authorities concerned that our organisation does not have any involvement in the firing incident last night."
In view of Thursday night's attack, security has been beefed up in the state with Chief Minister Sarbananda Sonowal directing all deputy commissioners and superintendents of police to remain alert.
"Strong action will be taken against the perpetrators of this dastardly violence. We will not tolerate such cowardly act," Mr Sonowal said.
Water Resource Minister Keshav Mahanta and Minister of State for Power Tapan Gogoi have reached Tinsukia.
Political parties and organisations across the state have condemned the killings and demanded that the culprits be immediately arrested.
A bandh, called by All Assam Bengali Federation, was being observed on Friday in the district, in protest against the attack.
Vehicles were off roads and shops were closed. No untoward incident was reported till 9 am, a police officer said.