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 on Thursday. "The rejection (of the clemency petitions) happened last week after the president returned from a foreign tour," presidential spokeswoman Archana Datta told AFP. The appeal sent to President Pratibha Patil by the three -- Murugan, Santhan and Perarivalan, all known by single names -- were their last hope of escaping the hangman's noose. The condemned men, who belonged to Sri Lanka's Liberation Tigers of Tamil Eelam (LTTE) militant group, are charged with plotting the May 21, 1991 killing of Gandhi by a female suicide bomber. The Supreme Court in 1999 confirmed the death sentences of the three men, but commuted the capital punishment to life in prison for Nalini Sriharan, an Indian Tamil woman who was also convicted. The three men sought a presidential pardon after the top court's verdict. A woman with explosives strapped to her body blew herself up, killing Gandhi instantly while he was on an election tour in the southern Indian town of Sriperumbudur. His shredded clothes and the shoes he was wearing at the time are on display in a museum in the Indian capital. 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 in India 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 at least 1,200 soldiers at the hands of the rebels. Rajiv's mother, former premier Indira Gandhi, was also assassinated in October 1984. One of the surviving killers was hanged. 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 May this year, however, President Patil unexpectedly 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.