The people have an allegiance with the two banned outfits, the sources said. Interestingly, NDFB is currently under truce with the security forces and is engaged with the government in peace negotiations.
"We have found that the Bangladesh-based HUJI has provided the expertise to ULFA and NDFB as none of them has the technology to explode such devastating bombs which claimed more than 80 lives," a Home Ministry official said.
Home Ministry sources said the government is worried over the fact that the northeast militants has started using a deadly mixture of RDX, ammonium nitrate and plasticised explosives to carry out explosions which led to greater casualties which was never seen in the past.
"At least 80 kg RDX were used to carry out the October 30 serial blasts in Assam. Never before in the northeast such a large quantity of RDX mixed with Ammonium Nitrate and plasticised explosives was used as propellants," a Home Ministry official said.
Each of the cars, which were used to carry out three explosions in Guwahati, was laden with 20 to 25 kgs of RDX. A maximum amount of explosives used for a single blast in the state was 10 kg at Dhemaji during the 2004 Independence Day which killed 13 people, including 10 school children.
The Sep 1 serial blasts in Agartala, where terrorists triggered four blasts within an hour, were the first synchronised explosions in the Northeast. The Assam serial blasts were carried out within a span of just 20 minutes.
"Kokrajhar, where three bombs were exploded is 250 km away from Guwahati while Barpeta Road, another place of bomb attack, is 150 km away. The near simultaneous explosions at the three far apart places show how the terrorists worked in precision," the official said, adding "this is also a new trend in the Northeast".
"Neither ULFA nor NDFB has the expertise to carry out such dead explosions. Besides, HuJI has no logistics at a place like Kokrajhar. So a nexus between local outfit with outsiders is evident," the official said.
The Oct 5 meeting of Chief Secretaries and Directors General of Northeastern states, which was attended by National Security Advisor M K Narayanan, Cabinet Secretary K M Chandrasekhar and Union Home Secretary Madhukar Gupta, took stock of the connection between a Naxal group and a Manipuri insurgent group, possibly to procure arms from the Northeast which has a porous international borders with several foreign countries, the sources said.
"Probably this is the first report of any Northeast militant group having link with an extremist outfit of mainland," the sources said. Unlike in the past, there have been growing collaborations among the different insurgent groups in the Northeast where most of the groups had links with dominant group NSCN but not among themselves.
"But now if a Tripura militant comes to Guwahati, it is ULFA which is providing him shelter and logistics," the official said.