NEW DELHI: India's Supreme Court commuted the death sentences Tuesday for three killers of former prime minister Rajiv Gandhi, citing delays in the case 23 years after he was assassinated by a Tamil suicide bomber.

The top court headed by Chief Justice P. Sathasivam handed the three life in prison on the grounds that successive Indian presidents had taken 11 years to decide their pleas for mercy against execution.

“We implore the government to render advice in a reasonable amount of time for taking a decision on mercy pleas,” Sathasivam told the court in announcing the judgement.

A lawyer for the three men — Murugan, Santhan and Perarivalan, all known by single names — hailed the judgement as “humane,” adding that they were now living in hope of one day being released from prison.

“There is hope that the convicts will walk out of jail. The remission will be decided by the state government of Tamil Nadu,” Yug Chaudhary told NDTV outside the court.

“It is time that the death penalty is abolished in this country,” he added.

The decision comes after the Supreme Court issued a landmark judgement last month that places new restrictions on executing prisoners in the world's biggest democracy.

The top court then commuted the death sentences of 15 convicts, ruling that “inordinate and inexplicable” delays in carrying out a death sentence were grounds for commuting a sentence.

The three at the centre of Tuesday's ruling were members of the Liberation Tigers of Tamil Eelam (LTTE), a Sri Lankan-based separatist movement, which was wiped out by Sri Lankan forces in 2009.

The men were convicted of plotting the May 21, 1991 murder of Gandhi by a female suicide bomber, but their appeal to the president in 2000 to spare them the hangman's noose was only finally rejected in 2011.

The lengthy delay contrasts sharply with the execution of Kashmiri Muslim separatist Mohammed Afzal Guru last year over a deadly raid on the Indian parliament in 2001 that left 10 people dead.

Successive governments in the world's largest democracy have long been wary of upsetting the large Tamil population in the south where the trio's case has become a cause celebre.

India had an eight-year unofficial moratorium on carrying out the death penalty from 2004 to 2012, with only three people executed in the last decade.

The delays have led to a build up of more than 400 prisoners on death row.

- Murder seen as retaliation -

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

His widow Sonia is the president of the ruling Congress party and his son Rahul is the frontman for the party's campaign in elections due by May.

The shredded clothes and the shoes that Rajiv was wearing when he was killed while on an election tour in the south of the country remain on display in a museum in the Indian capital.

Gandhi's killing was seen 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 Sri Lanka 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.

Amnesty International said Tuesday's decision piles pressure on the government to abolish the death penalty altogether.

“India must now do away with the death penalty — a cruel, inconsistent and irreversible form of punishment that has no proven deterrent effect on crime,” senior researcher Divya Iyer said in a statement.