The incident took place on May 4, a day after clashes broke out in Manipur.
Prime Minister Narendra Modi today said his heart was filled with anguish and anger over the horrific video of two women paraded naked in Manipur, which went viral on Wednesday, and said the guilty would not be spared.
"I want to assure the nation, no guilty will be spared. Action will be taken according to the law. What happened to the daughters of Manipur can never be forgiven," PM Modi said in his remarks before the start of the monsoon session of parliament.
"As I stand next to this temple of democracy, my heart is filled with pain and anger. The Manipur incident is shameful for any civilised nation. The entire country has been shamed."
The video that has triggered massive condemnation and demands for action shows two women being paraded naked by a mob in Manipur on May 4, a day after clashes broke out between the valley-majority Meitei and the hill-majority Kuki tribe in the BJP-ruled state over the Meiteis' demand for Scheduled Tribes (ST) status.
The women were molested and dragged to a field, where they were allegedly gang-raped.
The first arrest, 77 days after the incident, was reported today, a day after the video went viral.
While condemning the Manipur horror, PM Modi also referred to incidents in Congress-ruled Rajasthan and Chhattisgarh and said: "I appeal to all Chief Ministers to strengthen law and order in their state, especially regarding our mothers and sisters, and take strictest action, be it in Rajasthan, Chhattisgarh or Manipur. In every corner of India, we should rise above politics and act against heinous crimes."
Opposition parties have demanded the Prime Minister's statement in parliament over the Manipur horror. Some 15 MPs have put in notice to suspend all business for a discussion on Manipur.
Over 120 have died in the ethnic violence in Manipur and thousands have been internally displaced and are now living in relief camps.
