India's Supreme Court on Monday upheld death sentences handed down to three men over the gang-rape and murder of a woman in New Delhi in 2012, saying there were no grounds for a review.

"The review petition of all the three convicts has been rejected," A. P. Singh, a lawyer for the defendants, told reporters.

Jyoti Singh was raped by a gang of five men and a teenager on a bus. The case triggered angry protests by thousands of people as well as soul-searching about the country's treatment of women.

The six gang raped and tortured the woman with an iron bar as the bus drove loops through the Indian capital.

Singh was dumped on the streets 45 minutes later with horrific internal injuries, and died 13 days later in a Singapore hospital.

Four men were convicted in September 2013 for murder, gang rape, theft, conspiracy and "unnatural acts" after a seven-month trial in a fast-track court.

Only three of them were involved in the appeal rejected on Monday.

A fifth man, the suspected ringleader, was found dead in jail in a suspected suicide, while a 17-year-old was sentenced to three years in a detention centre and has since been released.