A man who was part of the mob that paraded naked two tribal women in Kangpokpi district of Manipur and was seen dragging one of them was among four persons arrested on Thursday as the incident of May 4 drew widespread condemnation.

In the evening, Chief Minister N Biren Singh briefed reporters that two persons have been arrested. Hours later, official sources said two more arrests have been made.

The grinding violence that has roiled Manipur for more than two months burst onto the national centrestage on Thursday as Prime Minister Narendra Modi and CJI D Y Chandrachud expressed deep anguish over a graphic video of two disrobed women being brutalised by a mob, calling the incident "shameful" and "unacceptable".

The incident in a village in Kangpokpi district that was captured in the 26-second video and stoked a nationwide outrage took place a day after ethnic violence erupted in the northeastern state on May 3 but the horrific footage surfaced only on Wednesday and became viral after the internet ban was lifted.

Hours after Prime Minister Modi in his first public comments on the Manipur violence vowed that no guilty will be spared and law will act with its "full might and firmness", Manipur Chief Minister N Biren Singh said the police have arrested two men. CJI Chandrachud also warned that the apex court will take action if nothing is happening on the ground.

Taking suo motu cognisance of the video, police last night said a case of abduction, gang rape and murder was registered at Nongpok Sekmai police station against unknown armed men.

The video capturing the ordeal of the two tribal women has become emblematic of the divide between the majority Meitei community and the Kuki tribal group, as political leaders cutting across party lines condemned the incident which also rocked Parliament on the opening day of the Monsoon session.

"Today, when I am standing by this temple of democracy my heart is full of pain and anger," Modi told reporters at Parliament complex amid criticism by opposition parties for not speaking on the ethnic violence in the BJP-ruled state.

"I want to assure the countrymen that no guilty will be spared. Law will act with its full might and firmness... What has happened to these daughters of Manipur can never be forgiven." The incident in the state is "shameful" for any decent society and it has insulted the entire country and the 140 crore countrymen are feeling ashamed, he added.

Chief Minister Biren Singh said a thorough investigation is underway and strict action, including possible capital punishment, will follow.

"It's a crime against humanity. We will not spare anyone," he told reporters in Imphal.

Tension mounted in the hills of Manipur after the May 4 video showed two women from one of the warring communities in the state being paraded naked by a mob from the other side.

The anguish over the incident found echo in the Supreme Court where a bench headed by Chief Justice of India Chandrachud took cognisance of the video and asked the Centre and the Manipur government to take immediate action.

It also said using women as instruments for perpetrating violence is "simply unacceptable in a constitutional democracy".

“We are very deeply disturbed by the videos which have emerged yesterday about the way those two women were paraded in Manipur," said the bench, also comprising Justices P S Narasimha and Manoj Misra.

"I think it is time that the government really steps in and takes action because this is simply unacceptable," the CJI said, adding, "We will give a little time to the government to act, otherwise we will take action if nothing is happening on the ground." He also termed it the "grossest" Constitutional and human rights violation, adding that the court is conscious of the fact that the video is of May 4 but that makes no difference.

The Centre also asked Twitter and other social media platforms to take down a video of the incident since the matter is being probed.

Sources said the videos were inflammatory, and as the matter is under investigation, Twitter and other social media companies have been asked to remove the video.

Senior BJP leader and former law minister Ravi Shankar Prasad said the party "condemns" the incident but said the surfacing of its footage on social media just a day ahead of Parliament's Monsoon Session is "surrounded by lot of mystery".

Proceedings in the Lok Sabha and the Rajya Sabha were disrupted and adjourned for the day with opposition MPs creating an uproar over the incident and demanding a discussion in Parliament.

Outside Parliament, opposition parties, including the Congress, Shiv Sena and DMK, took up the issue in a big way.

Hitting out at the government, Congress general secretary Jairam Ramesh said the prime minister had broken his silence on Manipur but it was “too little too late”.

Accusing the Centre of turning democracy into a "mobocracy", party president Mallikarjun Kharge said "humanity has died in Manipur" and asked Modi to speak about the ethnic violence-hit state in Parliament and tell the nation what happened.

Echoing him, Shiv Sena MP Priyanka Chaturvedi said, "This incident is shameful for the whole country. It is very disturbing." Hitting out at the Centre over the violence in Manipur, West Bengal Chief Minister and TMC supremo Mamata Banerjee said "mothers and daughters" of the country are crying after seeing the video.

The National Commission for Women(NCW) has taken suo motu cognisance of the incident and asked the Manipur state police chief to take prompt action in the matter.

Members of the Indigenous Tribal Leaders' Forum (ITLF) also staged a protest in the state.

One of the eyewitnesses to the May 4 incident, Hahat Vaiphei, claimed the villagers of B Phainom thwarted a similar attempt by a mob the previous day.

More than 160 people have lost their lives, and several have been injured since ethnic violence broke out in the state on May 3, when a 'Tribal Solidarity March' was organised in the hill districts to protest against the Meitei community's demand for Scheduled Tribe (ST) status.

Meiteis account for about 53 per cent of Manipur's population and live mostly in the Imphal Valley, while tribals, which include Nagas and Kukis, constitute 40 per cent and reside mostly in the hill districts.

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