NEW DELHI (AFP) - India's top court halted the freeing of four more killers of former premier Rajiv Gandhi on Thursday after a political uproar over a state government's plan to release all seven.

The Supreme Court in New Delhi issued a temporary restraining order against releasing the four who are serving life in jail over Mr Gandhi's assassination in 1991 by a Tamil female suicide bomber.

Prime Minister Manmohan Singh last week rejected the Tamil Nadu chief minister's moves to set all seven free, saying it was against all principles of justice as the murder was "an attack on the soul of India".

The court last week blocked the release of three of the men convicted of plotting the assassination, after Dr Singh's comments and his government's urgent legal action against the move.

Chief Justice P. Sathasivam issued the new order on Thursday, after hearing the government's arguments against releasing the other four, saying he needed time to examine the issues.

"There are two questions before us. The first is which is the correct government to decide on remission for these convicts and the second is whether the right procedure is being followed," Chief Justice Sathasivam told the court.

Mr Gandhi, whose widow Sonia is now president of the ruling Congress party, was targeted by Tamil Tiger separatists while he was campaigning in the southern state in May 1991 before an election.

His killing was seen as retaliation for a 1987 Indian government pact with Sri Lanka to disarm the Tamil guerrillas. India later withdrew its troops deployed to the island after losing 1,200 soldiers at the hands of the rebels.

Mr Gandhi became India's youngest-ever leader after his mother, prime minister Indira Gandhi, was assassinated in October 1984. He ruled until losing an election five years later.

His son Rahul, who is the Congress vice-president and the party's frontman for looming general elections, voiced his sadness last week over Chief Minister J. Jayalalithaa's decision to free the killers.

Critics have said the surprise decision was motivated by a desire to woo ethnic Tamil voters in her southern state for her regional party at the general elections due by the end of May.