Eleven Special Operation Group personnel were killed in Orissa on Sunday when Maoists blew up the van carrying them.
The attack happened at Govindapalli in Malkangiri district of Orissa.
Tragedy struck the first of the 3 vans carrying the jawans out to sanitise the only highway connecting Koraput with Malkangiri so that BSF battalions could get safe passage.
The powerful explosives were not planted under a culvert, as is the usual Naxal practice, but under a plain stretch of road on the Malkangiri-Koraput border.
Sources said a brief exchange of fire also took place between the security personnel and the rebels near the blast site.
"I strongly condemn the cowardly act of Maoists... it is savage and unlawful," said Naveen Patnaik, Chief Minister, Orissa.
Senior officials say the jawans violated the standard rule, to walk in files and not travel in vehicles on risky roads - something they have been taught time and again during their intensive training course.
And the blast comes as a rude jolt to the anti-Maoist drive, Operation Greenhunt that was to be launched across Malkangiri and Koraput districts only next week.
The attack comes as Home Minister P Chidambaram visited Lalgarh in West Bengal to take stock of the anti-Naxal operations there.
Discussing the larger picture of Naxal attacks there, Chidambaram said that the situation was most worrying in Jharkhand and Orissa. He also said the Maoists were cowards.