Assam Chief Minister Sarbananda Sonowal and Union Home Minister Rajnath Singh condemned the latest attack by the suspected United Liberation Front of Assam (Independent) -- Ulfa (I) in the state.

Chief Minister Sarbananda Sonowal promised strong action against those behind this dastardly violence.

"We will not tolerate such cowardly act," he was quoted as saying by the news agency PTI.

State ministers Keshav Mahanta and Tapan Gogoi along with DGP Kuladhar Saikia also rushed to the spot.

Home minister Rajnath Singh took Twitter said, "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."

The suspected Ulfa militants first kidnapped six young men from Kherabari area, near Dhola-Sadiya bridge under Sadiya assembly constituency in Tinsukia district of Upper Assam late Thursday.

The abducted persons were later gunned down near Brahmaputra river. Four of them died on the spot while one succumbed to injuries on the way to the hospital. Another injured person was taken to the hospital, informed Assam police ADGP Mukesh Agarwala.

The victims have been identified as Shyamlal Biswas, Ananta Biswas, Abhinash Biswas, Subal Biswas and Dhananjay Namsudra.

A massive counter-insurgency operation has been launched by the Army along the Assam-Arunachal Pradesh border while vigil has been intensified on the porous Indo-Myanmar border.

A dawn-to-dusk bandh against the killing of five people is being observed by various Bengali organizations in Tinsukia district today. West Bengal Chief Minister Mamata Banerjee has also extended her solidarity and announced that the Trinamool Congress would take out rallies in different parts of the state.

This is not the first ULFA attack in recent times. A low-intensity blast triggered by ULFA-I on October 13, which left four people injured at Guwahati's Sukleswar Ghat area on October 13.

The terror organization later termed it as a warning for Hindu Bengali groups working "against the interests of Assam".