NEW DELHI: India's Supreme Court on Friday stayed the execution of a Sikh militant convicted over a car bombing two decades ago, after his wife said he had developed mental illness while languishing on death row.

The Supreme Court announced it would review a plea for clemency for Devender Pal Singh Bhullar, who was convicted over a car bombing in the Indian capital that killed nine people and injured more than 20 in 1993.

“We want to know the present condition of Devender Pal Singh Bhullar,” Chief Justice Palanisamy Sathasivam told the court in New Delhi.

Bhullar's case is the first to be taken up by the Supreme Court since its landmark ruling earlier this month that places new restrictions on executing prisoners in the world's biggest democracy.

The top court commuted the death sentences of 15 convicts on January 21, announcing that “inordinate and inexplicable” delays in carrying out executions were grounds for reducing their original punishments.

The court ruled that mental illness was also grounds for commuting sentences of death row convicts, a ruling hailed by rights activists.

The court on Friday directed the hospital where Bhullar is being treated to file a report on his condition to determine if he was suffering from schizophrenia after spending two decades on death row.

The director of the hospital must “send a report of the medical condition of Devender Pal Singh Bhullar within a week,” the chief justice, who heads a four-judge panel looking at the case, said.

The court's order comes after it last year rejected his appeal for clemency, ruling then that neither his lengthy wait in prison nor his apparent mental problems were reasons to set aside the death sentence.

India's president has also rejected his mercy plea.

With more than 400 people on death row, the January 21 ruling is expected to have consequences for a huge backlog of cases.

India has carried out only three executions in the last decade following an eight-year unofficial moratorium from 2004 to 2012.

The ruling will also likely favour three men convicted over the assassination of former Indian Prime Minister Rajiv Gandhi who was blown up in 1991 by a woman suicide bomber.

Indian public opinion remains strongly in support of capital punishment, with celebrations held in November 2012 when Ajmal Kasab, a gunman from the 2008 Mumbai attacks, was put to death in the first execution in eight years.