Rights activists have been outraged by the Indian army's sentencing of two soldiers who killed a villager in custody in the restive northeastern state of Assam.

Major Nishant Sharma and rifleman Sudip Gurung were found guilty Monday by a military court of causing the villager's death in February, an army spokesman said.

"Sharma was sentenced to one year's forfeiture of service which will affect his promotion prospects and Gurung was sentenced to two months' rigorous military imprisonment," the spokesman said.

Lachit Bordoloi, an activist with rights group Manab Adhikar Sangram Samity, criticised the sentences.

"The punishment meted out to the two army men is nothing but an eyewash. Is this the nature of punishment given to people who murdered a man in cold blood?" he asked.

"The military court found them guilty but the punishment given to them is nothing but an attempt at hoodwinking the people," said human rights lawyer Nakib Zaman.

Witnesses alleged the villager, Ajit Mahanta, was shot dead after being picked up on suspicion of having links with the outlawed United Liberation Front of Asom.

His body was found in a sack dumped at a hospital in Dibrugarh town in eastern Assam the day after he was picked up.

The army claimed Mahanta was shot dead when he tried to escape.

The Assam government ordered a probe soon after the killing and demanded the soldiers be put on trial.

The killing sparked widespread public protests in eastern Assam, with police on one occasion opening fire and killing nine protestors. A paramilitary soldier was also stoned to death by angry protestors.