Home Minister Rajnath Singh addresses a press conference in Guwahati.
The massacre of over 70 tribals by Bodo militants in Assam was an "act of terrorism", Home Minister Rajnath Singh said on Thursday, and refused to hold talks with them "at any cost".
The National Investigation Agency or NIA will probe the militant attacks, he added.
After visiting some of the violence-hit areas in Kokrajhar and Sonitpur districts, the Home Minister told a press conference, "The violence is not merely a case of insurgency but one of terrorism. We are going to deal with this sternly."
He said the central government "will adopt a zero tolerance policy" towards terrorism and declared that "there would be no talks at any cost" with such militant outfits.
The comments from Mr Singh, who flew into Assam on Wednesday evening, came as the number of people who died on Tuesday in Kokrajhar, Sonitpur and Chirang districts surged to 73 on Thursday, officials said.
The minister asked the Assam government to take time-bound action and promised all help from the central government.
Mr Singh said 50 companies of paramilitary forces had been rushed to the state, and the army and Assam Rifles had been asked to cooperate with the police to control the situation.
He said the central government had taken up the issue of militants from India's northeast hiding in Bhutan and Bangladesh with the respective governments.
"One country has assured cooperation, and we are sure the other will also cooperate," he said.
Mr Singh today visited Sonitpur and Kokrajhar; he went to a few relief camps where hundreds have taken shelter after fleeing their villages. The Bodo militants had torched many homes.
The minister also met with security personnel deployed there.
Minister of State for Home Affairs Kiren Rijiju, who is from Arunachal Pradesh, and Tribal Affairs Minister Jual Oram have accompanied Mr Singh to Assam.
Rajnath Singh has already met Chief Minister Tarun Gogoi, Director General of Police Khagen Sarma, Chief Secretary Jitesh Khosla and other heads of security forces in the state.
The violence that ensued on Tuesday has been blamed on a hardline faction of the National Democratic Front of Bodoland (NDFB).