India's Supreme Court has released a man convicted of assassinating former Indian Prime Minister Rajiv Gandhi 31 years after his imprisonment.

The Supreme Court exercised emergency powers to release A. G. Perarivalan, his lawyer told CNN.

Perarivalan was arrested weeks after Gandhi was killed by a suicide bomber on 21 May 1991 in the southern state of Tamil Nadu.

The attack was blamed on separatist rebels fighting for the Tamil state in Sri Lanka. Gandhi's assassination was seen as retribution for his decision to send Indian troops to Sri Lanka in 1987 to enforce the peace deal and end the island's civil war.

Perarivalan, who was 19 at the time of the attack, was accused of buying batteries for the bomb. He was convicted of criminal conspiracy to commit murder, among other charges.

He was sentenced to death in 1998 along with six others, but in 2014 his sentence was commuted to life imprisonment.