The toll in the twin attacks in Assam rose to 27 Saturday. The state government decided to hand over the probe to the NIA while Prime Minister Manmohan Singh described it as a "cowardly attempt to spread fear and terror".
As many as 22 people were arrested in connection with the violence as seven more bodies were recovered Saturday.
Protesting against the attacks, a mob Saturday burnt down two camps of the state forest department in Baksa's Gobardhana area.
Manmohan Singh said the "attacks are cowardly attempts to spread fear and terror among our citizens".
"The government stands committed to fighting terror in all its forms," he said in a statement.
He added that his heart reaches out and grieves for all those who lost their near and dear ones and other affected people.
Chief Minister Tarun Gogoi said in Guwahati: "Since there is involvement of the NDFB (National Democratic Front of Bodoland) anti-talk faction militants, we have decided to hand over the probe to the NIA (National Investigation Agency)."
Violence erupted in the Bodoland Territorial Area Districts (BTAD) Thursday night when armed NDFB cadres opened indiscriminate fire in two villages. The second attack took place in Kokrajhar district Friday.
The violence has also led people to abandon their homes and take shelter in relief camps set up by district administrations.
The prime minister said the "people of Assam have been braving terrorist attacks with courage and fortitude in the past. They have voted in large numbers in the polling for the general elections and I am confident they will continue to fight terror resolutely".
The staggered elections in Assam for its 14 parliamentary constituencies took place April 7, 12 and 24.
Home Commissioner G.D. Tripathy told IANS: "Today (Saturday) morning, seven bodies were recovered from Salbari area in Baksa district."
"Armed assailants belonging to the NDFB anti-talk faction attacked two villages in Salbari area near the Manas National Park. Seven bodies have been recovered Friday night, seven more were recovered today (Saturday) morning," he said.
The victims included women and children, the home commissioner added.
"The situation appears normal as of now as there has not been any fresh incident of violence since yesterday (Friday) evening," said Tripathy.
Gogoi said the situation has slightly improved in Kokrajhar and Baksa district Saturday and there was no fresh incident of violence.
He said the state government has been doing its best to secure the lives of civilians in Kokrajhar and Baksa districts. Gogoi cancelled his scheduled visit to Germany following the violence.
There were conflicting views on what caused the violence.
Police suspect the attacks were in retaliation to the ongoing anti-insurgency operation by the security forces in the BTAD region, where some NDFB militants have been killed recently.
However, media reports Saturday said the violence could be linked to the voting pattern in the general elections.
Assam's Additional Director General of Police (Law and Order) A.P. Raut Saturday said curfew was relaxed for a few hours in Kokrajhar and Chirang districts. However, the indefinite curfew continued in worst-hit Baksa district.
He said that 22 people have been arrested.
"There has been adequate deployment (of security forces) and the army carried out a flag march for the second day today (Saturday) in affected areas...," Raut said.
Three companies of central paramilitary forces have already been deployed in each of the violence-hit districts. "More forces are coming and they would be deployed soon," he said.
