The 37-year-old man was arrested in the narrow bylanes of Ravi Dass Camp, a slum in southwest Delhi where four of the six accused lived, an officer in the city police control room said.

The low-grade device was filled with explosives usually used in firecrackers, he told AFP.

Two of the other accused come from outside Delhi, according to police.

The incident reflects growing anger across the country since the 23-year-old medical student was repeatedly assaulted and violated with an iron bar while being driven around in a bus on the night of December 16.

The suspects, some of whom were reportedly attacked in jail last week, are to be formally charged with rape and murder on Thursday.

The victim died of her grievous injuries in a Singapore hospital at the weekend.

Home Minister Sushilkumar Shinde has said the suspects risked the death penalty if found guilty and the case against them appeared very strong.