The Improvised Explosive Device (IED) that claimed the lives of ten policemen and a civilian driver in Dantewada district of Chhattisgarh on Wednesday had been planted by Naxals at least two months ago, police said.

Nine Naxal cadres belonging to the Darbha division of the outlawed CPI (Maoist) have been named in the First Information Report (FIR) registered at Aranpur police station regarding the blast, an official release said on Friday.

Preliminary investigation indicated that the IED was planted two months ago through "a foxhole mechanism" by digging a tunnel, said the release.

As it was buried three-four feet under the road, it could not be detected during demining exercises, said a senior official.

"Grass had grown on the layer of soil under which the wire connected to the explosive device was concealed,” Inspector General of Police (Bastar range) Sundarraj P told PTI.

Around 40-50 kg of explosive material was packed in the IED, he said.

Investigation is underway to find out how the IED remained undetected during the demining exercise conduced only a day before, he added.

As per the police's release, on the intervening night of April 25-26, District Reserve Guards (DRG) personnel of police from Dantewada and Chhattisgarh Armed Force (CAF) jawans from the Nahadi camp set out for an operation after learning that Maoists of Darbha division were present in the area.

Around 6:30 the next morning, an encounter took place between security personnel and Naxals near Nahadi, following which suspected militia members Lakhma Kawasi (30) and Sanna alias Kosa Madvi (25) were apprehended, it said.

Madvi sustained bullet injuries in his thigh and hand, it said.

When the duo was being taken back to Dantewada, Naxals detonated the IED near Aranpur around 1 pm.

When asked if there was any violation of the Standard Operating Procedure, the IG said the security personnel followed operational tactics.

"The apprehended Naxals were in the first vehicle (of the convoy). There was a long gap between each vehicle to avoid appearing like a convoy. The Naxals targeted the second vehicle with 10 (DRG) policemen onboard," the official said.

Around 200 metres before the attack site, some local tribal youths were stopping passers-by to collect money for Beej Pandum, a local festival, which is a usual practice, he said.

While they do not ask for money from the police, security personnel sometimes voluntarily give small sums for the festival. It was unclear whether the vehicle that was targeted had stopped there to give money to tribals, the official said.

A militia member might have been stationed in the area to keep a watch on the movement of the police personnel, and he or she might have alerted others when the convoy passed, the IG said.

Darbha division committee of Naxals has claimed responsibility for the attack in a statement and its commander Jagdish is instrumental in carrying out Naxal activities in the area, the official said.

A police official on condition of anonymity said security personnel did not think the route to be highly risky as road construction on the axis is complete up to Kamarguda, around 25 km away from Aranpur.

Teams of the Central Reserve Police Force (CRPF) and police have been combing the area following the incident, officials said.

The FIR regarding the blast was registered under sections 302 (murder), 307 (attempt to murder) and other relevant sections of the Indian Penal Code (IPC) besides provisions of the Explosive Substances Act, Arms Act and Unlawful Activities (Prevention) Act.

It named Naxal cadres Chaitu, Deva, Mangtu, Ransai, Jailal, Baman, Some, Rakesh, Bheema and others, the official release said.

A separate FIR was registered regarding the encounter that preceded the blast. It named Darbha division committee cadres Jagdish, Lakkhe, Linge, Somdu, Mahesh, Hidma, Umesh, Deve and others.

(Edited by : Sangam Singh)