New Delhi: The Central Bureau of Investigation (CBI) has taken over investigation of the case in which a gang of men sexually harassed a woman in Pollachi, Tamil Nadu, shot a video of the act and blackmailed her, officials said.

The agency has registered two FIRs against different sets of the accused; one for the sexual harassment of the woman and the second related to the assault on her brother.

The CBI began the probe as per the request of the Tamil Nadu government on March 12.

The gang is believed to have sexually harassed and blackmailed a large number of women in Tamil Nadu. The incidents triggered an outrage in the state when it came to light.

Citing the need for special attention, dedicated investigation with technical expertise and due to the severity of the crime, the government gave its consent to transfer the harassment and the related assault case from the state's CB-CID to the CBI.

The gang of four men had on February 12 allegedly tried to strip a woman inside a car near Pollachi, 500 kilometres from Chennai, and later blackmailed her with a video of the act.

The victim, who managed to free herself, filed a complaint with police officials on February 24.

The case assumed political overtones since a local functionary of the ruling All India Anna Dravida Munnetra Kazhagam (AIADMK) allegedly attacked the victim's brother.

The attack by the functionary, who was later expelled from the AIADMK, coupled with reports in a section of media that the gang had sexually harassed several other women, led to an outrage.

The issue eventually snowballed into a political row, and the main opposition Dravida Munnetra Kazhagam (DMK) targeted the AIADMK asking if it was protecting the accused persons.

A slew of protest demonstrations by parties including the DMK, students and the youth outfits had escalated the row, bringing more pressure on the government and police for quick action.

More visuals of the gang have surfaced on social media, heightening suspicion about them among the people, Coimbatore District Police had said.

The four accused in the sexual harassment case, Sabarirajan, Thirunavakkarasu, Sathish and Vasanthkumar are under judicial custody. They were booked under various sections of the IPC, Tamil Nadu Prohibition of Harassment of Women Act and the Goondas Act.

Nagaraj, the expelled AIADMK functionary, is one of the accused in the assault case besides Senthil, Babu, Manivannan and Vasanthakumar.

The CBI has taken over the FIRs and re-registered them as its cases as per protocol.