A third suspect has been arrested by police on Tuesday in connection with the gang rape of her cousin, a trainee nun, in the Indian state of Odissa.

The suspect, identified as 31-year-old Nalini Sobhasundar, was arrested in an area bordering the districts of Kandhamal and Gajapati, on suspicion of planning the attack.

Her relatives Jotindra and Tukuna have also been arrested on suspicion of carrying out the rape of their 22-year-old cousin, who was training at the St Mary's Convent in Chennai.

It has not yet been disclosed how the three suspects are related.

Nalini is alleged to have lured the victim away from Chennai by ringing her up and telling her that her mother was seriously ill.

The victim boarded a train back to her hometown of Berhampur, where she was picked up by Jatindra and Jogendra.

The two men allegedly took their victim to an isolated place and gang-raped her with a third unidentified man, for about a week.

The victim was eventually dropped off at the railway station by her rapists, with threats of dire consequences if she revealed the incident to anyone. Once home she narrated her ordeal to her mother, who lodged a police complaint.

The Times of India reports that the third rapist remains at large.

Though the exact motive behind the crime is unknown, family rivalry is thought to be the reason - police have revealed that the victim's brother is accused of murdering the father of one of the rapists.

"We are investigating the motive behind the fake call and involvement of others in the case," Singh said.

The case is set to be transferred to the government railway police of Berhampur, since the crime took place under their jurisdiction.

A bail application for Jatindra and Jogendra, who are currently in detention, has been rejected.