100-150 kg of the explosive was used, shows probe.

An analysis by the National Security Guard of the scene of attack in Pulwama, 30 km from Srinagar, has established that the SUV (sports utility vehicle) driven by the suicide-bomber was packed with RDX, a type of high explosive.

A senior government official told The Hindu that preliminary investigation suggested that 100-150 kg of RDX was used in the attack on the CRPF convoy on Thursday. Samples had been collected for forensic analysis, he said.

Jaish-e-Mohammad's Adil Ahmed Dar's vehicle rammed a bus in the convoy, killing 40 personnel. The CRPF had been moving such convoys, comprising more than 2,500 personnel each, on the Srinagar-Jammu highway. In the past fortnight, two such convoys had moved from Jammu to Srinagar. The latest was on February 4 with a convoy of 91 vehicles and 2,871 personnel.

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Dar entered the highway from a slip road (from the Kakapora-Lelhar side) and hit the bus, the fifth in the convoy, from the left side, preliminary investigation shows. The road was open for movement of civilian vehicles, and an hour back, the route was sanitised for the presence of improvised explosive devices. More than 2,000 men were deployed for road security, an official said.

Most men killed were returning from their annual holiday.

The senior government official said convoys ran smoothly during summers but were irregular during winters and the monsoon because of snowfall and landslips. Hence, CRPF personnel get stranded in Jammu for days. “As the transit camp has a limited capacity to accommodate only 1,000 personnel at a time, the number of stranded transients exceeds 3,000-4,000,” he said.

The official pointed out there was no facility for transporting them by air so they have to depend on the road to move from Jammu to Srinagar and back.

“As the number of personnel at the transit camps always remains high, buses are used for transportation. These buses have thin metallic plates which offer no protection from bullets or IEDs. Firing being the main threat, improvised plating has been arranged in a few vehicles but there is no safety against IEDs,” an internal note of the Home Ministry said.

The official said troops have been sensitised for stand-off firing and IEDs planted conventionally but were caught off guard by this kind of suicide attack.

“There was an input from the J&K police last week about IED blasts, but it was not specific in nature,” he said.