NEW DELHI: A 17-year-old youth who is being tried in a juvenile court over the fatal gang-rape of a student on a bus in New Delhi was formally charged with murder on Thursday, legal sources said.

The teenager, who cannot be named for legal reasons, was accused of playing a key role in the murder, rape and robbery of a 23-year-old medical student last December in the Indian capital.

Five adults are also being tried in a separate fast-track court.

Two sources, speaking on condition of anonymity due to a wideranging gagging order, said the minor was present before the judge when the charges were framed.

"The minor has been charged with rape, murder, criminal conspiracy and unnatural sex by the court and he has pleaded not guilty," one person closely involved in the case told AFP.

A second legal source confirmed that the charges had been put to the teenager on Thursday morning and that he had entered a not guilty plea.

Under Indian law, the youth faces a maximum of three years in a detention facility if convicted -- a sentence limit that has caused widespread anger.

The victim's family has been among those calling for the juvenile to be tried alongside the five other accused, who face the possibility of being hanged if found guilty of murder.

But the Juvenile Justice Board accepted the school records of the teenage suspect, which states that he was born on June 4, 1995, making him 17.

A parliamentary committee voted on Wednesday against a proposal to lower the age of adult criminal responsibility to 16.

The dead woman, a physiotherapy student, suffered massive intestinal injuries during the assault on December 16 in which she was raped and violated with an iron bar.

She died 13 days later after the government flew her to a Singapore hospital in a last-ditch bid to save her life.

Her male companion also suffered serious injuries during the assault.