Guwahati/Dhubri, Aug. 10: The army last night stumbled on Ulfa’s improved striking prowess — two double-detonator IEDs that diminish the possibility of failed explosions.

Found on a Cooch Behar-Bilasipara bus at Gouripur last night, the IEDs can be programmed in a manner that if the first detonator failed to trigger the explosion, the second one will get activated automatically.

“This enhances the precision of the IEDs as well as making deactivation very risky. Timer devices are generally very erratic. Many a times they fail to explode because of a problem in programming. But in this kind of device, if one programme fails, it automatically activates the other,” an army explosive expert said.

The army said the recovery has opened up a new challenge for the security apparatus in Assam, which has already been put on a full alert to foil Ulfa’s attempts to “avenge” the reverses it suffered when members of its most potent 28 battalion broke away.

Although it was not clear if the explosives were meant to be used in the run-up to Independence Day, the outfit today called for a boycott of celebration and a general strike in the state on August 15, like it does every year. Sources said the “dilapidated Ulfa” in a desperate bid, was joining hands with jihadi groups to make its presence felt in Assam.

“Security forces have been put on full alert since we have reports of the Ulfa leadership issuing instructions to its cadres to carry out blasts and other subversive activities on the run to August 15,” a senior police officer said.

The officer said a number of militants arrested recently revealed during interrogation that the Ulfa leadership wanted to prove that the outfit still has enough striking power despite two of its companies declaring a truce.

Inspector-general of police (special branch) Khagen Sharma said 109 and 709 battalions of Ulfa, which are operational in Lower Assam districts and the capital city are more influenced by the ISI and would make attempts to sabotage August 15 celebrations. The government spokesperson Himanta Biswa Sarma, too, admitted of the growing threat perception.

Sarma, however, said the security personnel were prepared to foil any attacks.