A graphic video showing two women forced by a baying mob to walk naked in the northeastern Indian state of Manipur has sparked outrage after it emerged on social media and prompted the country's leader Narendra Modi to break his silence on the months-long sectarian conflict tearing the state apart.

The viral video depicts an incident from May 4, according to the Indigenous Tribal Leaders' Forum (ITLF) but police only made arrests once the footage went online this week.

Manipur Police described the incident on Twitter as "a case of abduction, gang rape and murder" on Wednesday.

Officials said Thursday that four people have been arrested and that police raids are ongoing. Authorities are interrogating more than three dozen men in relation to the apparent sexual assault, Reuters reported.

The video, which has been seen by CNN, shows two terrified women being forced to walk naked through a crowd of clothed men. The victims appear to be being groped and sexually assaulted while surrounded by a mob of men, many brandishing long canes or sticks as weapons.

The horrific footage emerged amid ongoing ethnic violence in the northeastern Indian state.

Modi addressed the situation in the state for the first time on Thursday, saying: "My heart is filled with grief and anger. The incident in Manipur is shameful for any civil society."

"What happened with the daughters of Manipur can never be forgiven," Modi continued, adding the "law will take its course with all its might."

The Upper House of Parliament was adjourned minutes into reconvening after opposition MPs sparked an outcry over the refusal to discuss the issue of Manipur.

The ITLF issued a statement on Wednesday, writing: "A video which went viral today shows a large Meitei mob parading two Kuki-Zo tribal women naked toward a paddy field to be gang-raped."

The statement continued saying the "despicable incident" took place in B. Phainom village in Kangpokpi district and "shows the men constantly molesting the helpless women, who cry and plead with their captors."

In recent months, Manipur has grappled with violence. Clashes broke out in the state capital Imphal on May 3 after thousands of students, mostly from the Kuki tribe, took part in a rally against the majority Meitei ethnic community, who have petitioned for special tribal status. Among other things, tribal status would enable the Meitei to buy land and provide more opportunities for government jobs.

Over 100 people have been killed and tens of thousands more displaced since then.

The incident on May 4 occurred after the women's village was burnt down and two men were beaten to death, according to the ITLF.

India's main opposition Congress party has been a vehement critic towards Modi's handling of the issue, with the party's president Mallikarjun Kharge tweeting Thursday, before the opening of Parliament: "Humanity has died in Manipur. Modi Govt and the BJP has changed democracy and the rule of law into Mobocracy by destroying the delicate social fabric of the state."

Tagging Modi, his tweet continued: "India will never forgive your silence. If there is any conscience or an iota of shame left in your government, then you should speak about Manipur in the Parliament and tell the nation on what happened, without blaming others for your dual incompetence -- both at the Centre and the State."

Soon after, the state's chief minister, N. Biren Singh, tweeted that an arrest had been made.

"After taking a Suo-moto cognisance of the incident immediately after the video surfaced, the Manipur Police swung to action and made the first arrest this morning," he wrote. Suo-moto cognisance is a procedure in Indian law allowing the court to take action in a case without a complaint being filed.

He added that "a thorough investigation is currently underway and we will ensure strict action is taken against all the perpetrators, including considering the possibility of capital punishment. Let it be known, there is absolutely no place for such heinous acts in our society."

Manipur police later said that it had made three more arrests of people accused "of the heinous crime of abduction and gang rape."

The Indian government has issued an order to Twitter and other social media platforms, instructing them not to share the viral video, a source familiar with the matter told CNN Thursday, adding it is "imperative for social media platforms to adhere to Indian laws as the matter is currently under investigation."