At least one vehicle at the front of the convoy was then hit by a land-mine blast before as many as 200 suspected rebels opened fire, they added.

BBC: India probes deadly Maoist ambush in Chhattisgarh

Along with jammers, troops use air surveillance, robots, blast-resistant vehicles and mine rollers as countermeasures.

CNN: Jamming systems play secret role in Iraq

Specialist mine rescue crews, ambulances and helicopters rushed to the mine as soon as the blast was reported.

BBC: New Zealand miners missing after explosion