The executions of four men over the notorious 2012 gang-rape and murder of a student in India's capital inched closer Wednesday after the top court rejected a death sentence review petition by one of those convicted.

The four men attacked a 23-year-old woman on a bus in Delhi as she returned from the cinema in December 2012 in a case that sparked outrage and horror in India and across the world.

The student died two weeks later from extensive internal injuries amid nationwide protests by tens of thousands of Indians who took to the streets to call for justice.

On Wednesday, the Supreme Court ruled there were no grounds to hear a review petition by Akshay Kumar Singh, the last of the four to bring such a plea.

Their options now to avoid the gallows include filing a final petition to the Supreme Court and appealing for mercy to the Indian president.

Six people were originally held but one of them died in prison, allegedly by suicide, while a sixth, a minor at the time of the attack, was released in 2015.

Indian media reports in recent days have said that Tihar jail in Delhi, where the men are held, recently held a dummy execution.

The victim's family welcomed the court's latest decision.

"We are happy that the execution is now one step closer," her mother told reporters.

The fact the physiotherapy student survived long enough to help police identify her attackers made her a symbol of India's struggle against widespread sexual violence.

Her case led to a major overhaul of laws surrounding sexual assault.

Singh's unusual plea argued that there was no need to hand him the death sentence as New Delhi's air and water pollution were already killing him.

His lawyer, A.P. Singh, said the review plea was rejected because of pressure from the public.

India