Former Indian PM Gandhi's killers to hang

India's president has rejected mercy pleas from three men convicted of the 1991 assassination of then prime minister Rajiv Gandhi, paving the way for their execution, an official told AFP.

The appeal, sent to President Pratibha Patil by the men -- Murugan, Santhan and Perarivalan, all known by single names -- was their last hope of escaping the hangman's noose.

All three belonged to Sri Lanka's Liberation Tigers of Tamil Eelam (LTTE) militant group, which was accused of plotting the May 21, 1991 murder of Gandhi by a female suicide bomber.

Gandhi had become India's youngest ever prime minister after his mother, former premier Indira Gandhi, was assassinated in October 1984, and ruled until losing an election five years later.

The shredded clothes and the shoes he was wearing when he was killed while on an election tour in the southern of the country 20 years ago remain on display in a museum in the Indian capital.

"The rejection (of the clemency petitions) happened last week after the president returned from a foreign tour," presidential spokeswoman Archana Datta told AFP.

Although the Supreme Court upheld the original death penalty verdict for the three convicts it later commuted the capital punishment to life in prison for Nalini Sriharan, an Indian Tamil woman who was also convicted.

The three men had sought a presidential pardon after the top court's verdict.

The LTTE, wiped out by Sri Lankan forces in 2009 following a bloody offensive by government troops on the island, always denied its hand in Gandhi's assassination.

But the militant group's now-slain leader Velupillai Prabhakaran went on to honour the assassin's father as a "great person who contributed to the Tamil cause."

Gandhi's killing was seen at home as retaliation for a 1987 Indian government pact with the Sri Lankan government to disarm the guerrillas, who had been trained and armed by New Delhi in the early 1980s.

After that pact, the LTTE fought Indian troops deployed to the island by Rajiv Gandhi's government to supervise the accord. India withdrew its troops after 32 months in which it lost 1,200 soldiers at the hands of the rebels.

Ten Indians and nine Sri Lankans sentenced to death by a lower court for their involvement in Rajiv Gandhi's assassination were freed after they were acquitted by the Supreme Court in 1999.

The last execution in India was in 2004 when a 41-year-old former security guard was hanged for the rape and murder of a 14-year-old schoolgirl in Kolkata city.

An anti-death penalty lobby group condemned the rejection of the clemency petition.

"It has been well established that capital punishment does not help to reform society," said Kirity Roy of the privately-run South Asia Network Against Torture and Impunity.

"If India wants to portray itself as a civilised nation and aspires to fulfil its obligations to international norms then it must abolish the practice," Roy told AFP by telephone from Kolkata.

"There were 12 rapes almost immediately after the guard's hanging and so it proves the death sentence is not a deterrent," argued Roy, urging President Patil to re-think her decision.

In May, Patil rejected a mercy petition from a murderer in the northeastern state of Assam, leaving the state scrabbling to find a hangman.

Many of the small number of known hangmen nationwide have either died or retired in recent years.