A special court in India has sentenced 47 policemen to life in prison for killing a group of Sikh pilgrims in 1991 whom they had claimed were militants.

The officers were convicted of shooting dead the pilgrims to try and earn promotions in Uttar Pradesh state, which was hit by Sikh militant activity at the time, the Press Trust of India (PTI) said.

Prosecutor SC Jaiswal said the police stopped a bus carrying the pilgrims and their families before later marching 11 of them into a jungle area and carrying out the killings.

"The court observed that there was ample evidence to award life sentences to the guilty," Mr Jaiswal said on Monday.

"The court specifically observed that a crime of such magnitude could not have happened without the knowledge of those higher up and they too should have been charged."

The court of the Central Bureau of Investigation (CBI), India's leading investigative agency, found the police guilty of carrying out a "fake encounter".

The term is commonly used in India for staged confrontations, in which police or military forces execute unarmed suspects and later claim it was self-defence.

At the time of the killings, militants were fighting in the region to try to create a Sikh homeland called Khalistan.

The Supreme Court, acting on a lawyer's petition, ordered the CBI to investigate the case.

The CBI charged 57 police in 1995, but 10 of them died during the eventual trial that took years to conclude in India's notoriously slow legal system.

AFP