India's Supreme Court will hear a motion to stop the assassins of former Prime Minister Rajiv Gandhi being freed, according to local reports.

The move comes after the Supreme Court on Thursday prevented the release of three of the seven people convicted, their death sentences commuted to life in prison because of a lengthy delay in a decision on their mercy plea.

The court ruled on Thursday that the three were on death row and could not be released by the chief minister of Tamil Nadu state, The Guardian website reported.

The other four convicts could still be freed, according to the Tamil Nadu government. Monday's hearing will aim to stay the release of these four convicts as well, according to local media reports.

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Last Wednesday, Tamil Nadu Chief Minister J Jayalalitha made the announcement to free the seven. A day earlier, the Supreme Court had commuted the death sentences of the three to life in prison.

Supporters of the late Rajiv Gandhi and the Indian National Congress (INC) spoke out against the move.

Prime Minister Manmohan Singh said last week that freeing the convicts would be contrary to all principles of justice, as Rajiv Gandhi's assassination was "an attack on the soul of India".

The convicts have spent more than 20 years in jail. One of them, who was earlier on death row, was shown mercy after the intervention of Rajiv Gandhi's widow and Congress president Sonia Gandhi.

Rahul Gandhi, the Indian National Congress vice president and the son of Rajiv Gandhi, told reporters he was saddened by Jayalalitha's decision.

"I am saddened," he said. "It is not just about my father, the killers of this country's prime minister are being released."

Rajiv Gandhi was assassinated in 1991 by a woman from the Sri Lankan Tamil group LTTE, or the Tamil Tigers, who detonated a bomb whilst greeting him during a rally in Sriperumbudur in Tamil Nadu.

For years, the case has been linked to Tamil sentiment and all regional parties in the state have campaigned for the convicts' release, NDTV said.