A 16-year-old tribal girl was allegedly gang-raped by four “unknown” youths on the bank of the Kopai river in Birbhum’s Santiniketan on early Friday morning.

The incident further embarrassed the state administration at a time when the Opposition was scaling up the attack on the Mamata Banerjee government on women’s safety in Bengal.

Police sources said the four youths had first beaten up a male friend of the girl and then taken her away to a lonely place where they gang-raped her.

“We have started a case of gang-rape according to the statement of the girl, who is now in the hospital. The elder sister of the victim had also lodged a complaint. The victim could not give us any names, but we are trying to identify the accused persons. An artist has been asked to draw the sketches of the suspected persons according to the description of the victim and her friend,” said Nagendra Nath Tripathi, the Birbhum police chief.

The incident, multiple sources in the police said, prompted the Nabanna top brass to instruct the district police to fast-track the investigation and arrest the accused.

“We are doing our best to nab the culprits as soon as possible. The male friend of the minor girl is being interrogated to know few details about the accused,” said a senior police officer.

Nath Tripathi reached the spot within an hour, along with senior police officers.

Around 11.30am, the additional DG (western range), Sanjay Singh, and DIG Burdwan range Bharatlal Meena reached the spot. Sources said the police had begun using tower dumping technology to try and zero in on the four persons.

Several police officers said as the incident in Santiniketan had come within a week of the gang-rape of a Class IX girl at Hanskhali in Nadia district, they were under pressure.

“There is a clear instruction from Nabanna top brass to complete the investigation without any delay and we are working accordingly,” said a senior IPS officer.

According to the police, the tribal girl had come to visit her uncle’s place from a nearby village in Santiniketan. She went to Charak Mela (a rural fair organised every year on the last day of the Bengali calendar) with her friend. As the fair went on through the night, she attended a cultural programme with her friend.

“Around 1.30am, the girl went to the bank of the river with her male friend. The four persons came and attacked them. They beat up the male friend, who is a minor, and took away the girl. They raped the girl repeatedly there,” said a police officer.

After the incident, the girl went back her home and narrated the incident to her family, said a police source while adding that they had come to know about the incident around 8am.

“The girl has been admitted to the hospital for a medical test. Her health condition is stable,” said a police officer in Santiniketan.