As the Indian Home Minister Rajnath Singh landed to assess the violence, separatist Bodo militants opened fire and burned houses in Assam's Udalguri district, the Press Trust of India reported, quoting senior district police officer Bir Bikram Gogoi.
Separatist Bodo militants are suspected to have started the attacks on Tuesday, which have mostly targeted the Adivasi minority.
“Assam violence is an act of terror and we will deal with it accordingly,” Singh said in a firm message to militants from the National Democratic Front of Bodoland (Songbijit), before leaving for Assam.
Singh chaired a high-level security meeting in New Delhi, attended by top security and defence personnel, in which a decision to launch an offensive against the Bodo militants was taken, local newspaper Times of India reported.
A counter insurgency operation is underway as the federal government rushed 5,000 paramilitary forces to the affected areas.
Assam chief minister Tarun Gogoi said on Wednesday that 2,000 paramilitary troops have already reached Assam.
Gogoi said that the militants have shelters in neighboring country Bhutan and Myanmar and Indian state of Arunachal Pradesh.
“We cannot act on these areas and I will be asking the home minister to take up the issues with other countries and our neighboring states,” Gogoi said in a press conference.
“We are going all out against the militants. I had a discussion with Prime Minister last night and the Centre [federal government] has given directives to the Army to take out these militants,” he said.
A high alert has been issued in the tea-growing state and the Indo-Bhutan border in north Assam has been sealed. An indefinite curfew has been clamped in Kokrajhar in western Assam and Sonitpur in the north to control the worsening situation.
SN Singh, senior state police official in-charge of law and order, said that the breakaway group of the National Democratic Front of Bodoland was behind the brutal killings.
Meanwhile, activists belonging to the All Assam Students Union sat in a silent protest with their mouths tied with black cloths in Guwahati.
Assam governor Padmanabhan Balakrishna Acharya, who was in West Bengal, cut short his visit to head back to Assam as the crisis deepened.
The death toll rose sharply on Wednesday as state police officials recovered scores of dead bodies from deeply-forested area in and around Sonitpur and Kokrajhar districts.
The Bodo militants killed over 60 Adivasis, 37 in Sonitpur and 25 in Kokrajhar, in a well-coordinated attack at five different places on Tuesday evening.
The dead included 21 women and 18 children.
Five Adivasis were killed in police firing on Wednesday as they protested and clashed with police with bows and arrows and blocked a national highway.
Television images showed people protesting by burning tyres and blocking trains on railway track.
They took to the streets after they were targeted in killings by the NDFB (S), an armed group that wants autonomy for the Bodo-speaking people.
Angry Advasi protestors killed two from Assam’s Bodo ethnic group in retaliation.
The protesters allegedly set fire to house belonging to the Bodo community in the Sonitpur district and attacked a local police station.
Sonitpur was the worst-affected with 13 children and 10 women killed in Tuesday's attack.
Adivasis, who are compromised of various ethnic and tribal minorities, originally hail from central India and work in Assam's famous tea gardens.
Survivors of the deadly attack told police that militants knocked on their doors on Tuesday wearing army uniforms and armed with automatic rifles. The militants asked for water and indiscriminately opened fire on Adivasis.
The targeted killings of Adivasis is being seen as a “retaliation” to the counter-insurgency operation by the state police which killed two Bodo militants on Sunday.
Adivasis were targeted as Bodo militants suspect that the people from the minority group may have passed on information to security agencies about its cadres.
Tuesday’s attack is the year’s worst attack by Bodo militants. In June, suspected Bodo militants killed over 40 Bengali-speaking Muslims in Kokhrajhar and Baksa districts of Assam.
In 2012, over 100 people died and 4,50,000 displaced as Bodos targeted Bengali-speaking Muslims, one of the deadliest massacres in Assam.
Tuesday’s massacre is the second major ethnic clash between Bodos and Adivasis since 1996.
The Bodos, an indigenous tribe in Assam, constitute 10 percent of the state’s 33 million population.