India's prime minister asks state gov't not to free 7 convicted in Rajiv Gandhi assassination

India's government has asked the Supreme Court to stop the state of Tamil Nadu from releasing seven prisoners serving life sentences for the 1991 assassination of former Prime Minister Rajiv Gandhi.

The state ruled Wednesday that the seven should be released because they have served more than 20 years in prison.

On Thursday, Prime Minister Manmohan Singh asked the state not to free the convicts, saying it "is not legally tenable" to release them.

The federal government also asked the Supreme Court to intervene.

Gandhi was killed by an ethnic Tamil suicide bomber in Tamil Nadu in May 1991 as he campaigned for a return to the post of prime minister.