A police spokesman said militants triggered an explosive device by remote control when a Central Reserve Police Force convoy was passing a village about 570 kilometres (350 miles) east of Assam's main city of Guwahatil.
"The convoy was returning from a routine patrol when the explosion took place. The vehicle was damaged in the blast," a senior police official told AFP by telephone from Assam's Tinsukia district where the blast occurred.
A trooper was killed on the spot and four others received serious injuries, he said.
"The injured were shifted to a nearby hospital," said the official, who wished not to be identified.
Police blamed the blast on the outlawed United Liberation Front of Asom (ULFA), a rebel group fighting for an independent Assamese homeland since 1979.
"The area is dominated by the ULFA and there is no doubt that the blast was carried out by them," said the police official.

Copyright AFP (Agence France-Presse), 2006