The Centre on Wenesday directed the Assam government to nab the "ring leaders" involved in ethnic violence in the state but ruled out a Bangladeshi hand in the trouble which so far has claimed 40 lives.
Union Home Secretary RK Singh also said 2,000 central security personnel have been deputed to guard Guwahati-bound trains and railway tracks which were disrupted.
"We have asked the state government to book ring leaders of both sides so that violence can be checked immediately. No one involved in the violence will be spared," Singh said.
Asked about claims that some people involved in the clash might have links with neighbouring Bangladesh, Singh ruled out the possibility of involvement of anyone from across the border.
"The international border is sealed. It is simply impossible for any organised group crossing over to India from across the border to carry out the attacks," he said.
He said 1,000 paramilitary personnel and 1,000 Railway Protection Force personnel have been deputed to guard Assam-bound trains and tracks for smooth running of trains to the northeast.
Singh said 2,500 paramilitary personnel have reached Assam to assist the local administration while 2,300 more men will reach the state tonight.
"Another 15 companies (1,500 personnel) are on their way," he said.
The Home Secretary said steps are being taken to stop the violence from spreading to other districts.
He said Prime Minister Manmohan Singh is in constant touch with home minister P Chidambaram, who is briefing him regularly.
National Disaster Response Force personnel were assisting the state administration to relief operations, he said.
The death toll shot up to 40 with the recovery of eight more bodies today. Train services of the North East Frontier Railway partially resumed in the affected sections.
Five more bodies were recovered from Bijni in Chirang district and three from worst-hit Kokrajhar where shoot-at-sight orders and indefinite curfew were in force, police said.
Assam government officials informed the Home Ministry that the violence has spread to more than 400 villages located in 8,000 sq km areas in trouble-torn Bodoland Territorial Administered Districts.