She said her government will provide all necessary co-operation and assistance to the CBI for investigation in this case.

"Considering the seriousness and sensitivity of the case and also the fact that the place of incidence is very close to border area, I have decided to entrust investigation of the case to CBI", the Chief Minister said in a Facebook post.

READ MORE: PM Modi expresses concern over nun gangrape

"The Ranaghat incident of 14th March, 2015 is a very serious matter. The police administration was instructed to take swift action to nab the culprits. They are making their best efforts", Banerjee said.

A 71-year-old Sister Superior of a convent school was allegedly gangraped by dacoits at the Gangnapur school in Ranaghat subdivision of Nadia district on Saturday after which a CID probe was ordered into the incident.

Nuns take part in a candle light march to protest against the gangrape of a nun in Nadia district of West Bengal

MUST READ: Angry protesters block CM Mamata Banerjee's convoy at Ranaghat   

Fifteen persons have been detained in this connection so far.

Meanwhile, National Human Rights Commission (NHRC) on Wednesday issued a notice to West Bengal government seeking a report in connection of the alleged gang rape of a nun in the state.

According to an official statement released on Wednesday, NHRC has issued notices to the Chief Secretary and Director General of Police, West Bengal calling for reports in the matter within two weeks.

ALSO READ: 10 detained in nun rape case

The notice was issued after the commission took suo motu cognizance of a media report that a 71-year-old nun was raped by a gang of seven dacoits inside a Convent in Gangnapur village of Nadia district in West Bengal on March 14.

West Bengal CM Mamata Banerjee surrounded by locals as she comes out of the hospital after meeting a nun who was seriously injured after gang rape

The Commission has observed that the contents of the press report, if true, amount to serious violation of human rights of victim.

Latest News from West Bengal News Desk