Amnesty International urged India to halt its first scheduled execution for eight years and to impose an official moratorium on any further use of capital punishment.

In an open letter to Prime Minister Manmohan Singh, the human rights watchdog said the execution of Balwant Singh Rajoana, slated for March 31 in the northern state of Punjab, would be a major step backwards.

Rajoana was sentenced to death in 2007 for his role in the 1995 assassination of the then Punjab chief minister, Beant Singh.

"Resuming executions after an eight year hiatus would place India in opposition to regional and global trends towards abolition of the death penalty," said Amnesty's Asia-Pacific director Sam Zarifi.

"We urge you to stop the execution of Balwant Singh and establish an official moratorium on executions ... and swiftly abolish the death penalty in India for all crimes," Zarifi wrote in his letter to the prime minister.

If Sunday's hanging goes ahead in Punjab's Patiala Jail, it would be the first execution in India since 2004, when a former security guard was hanged for the rape and murder of a 14-year-old schoolgirl.

India has hundreds of condemned convicts awaiting execution, including the killers of former prime minister Rajiv Gandhi, and Pakistani national Mohammed Ajmal Amir Kasab -- the sole surviving gunman from the 2008 Mumbai attacks.

A complex and lengthy appeal process means those sentenced to die often sit on death row for many years.

In most cases the death sentence is commuted to life imprisonment.