Army spokesperson Abhijeet Mitra told CNN that 26 units had been deployed to Assam, while three were sent to Tripura. There are approximately 70 soldiers per unit.

'We demand justice'

Mehraj Khan, whose friend was one of the young men killed, said at the time that they were walking back from where a procession had been taking place "and suddenly six vehicles ... stopped nearby and they threw a stun grenade to disperse the protestors."

"As soon as they threw the stun grenade, they switched off their car light and ... started firing," he said.

Khan said he saw his friend's blood and brains on the ground after the incident.

A relative of one of the men shot said the police reaction was unwarranted: "We demand justice, are we not Assamese citizens, why shoot own people?"

About 1,800 people have been detained in Tripura since Wednesday, according to Rajiv Singh of the Tripura police force.

Thousands defied a government curfew Thursday to attend a meeting announced by the All Assam Students Union (AASU), which is also organizing the hunger strike.

With large numbers of troops on the streets and communication disrupted, residents could be seen stocking up on necessities like milk and eggs in grocery stores, amid fears of further chaos.

Controversial legislation

CAB promises to fast-track citizenship for religious minorities, including Hindus, Sikhs, Buddhists, Jains, Parsis and Christians, from Afghanistan, Bangladesh and Pakistan. But the exclusion of Muslims -- which Modi says is because they are not minorities in India's neighbors -- has raised concerns about the bill's constitutionality and the growing anti-Muslim rhetoric in India.

"There is a short-term and long-term objective to polarize India's voters on the basis of religious lines," said Harsh Mander, a human rights activist and author. "The BJP and its ideological partner Rashtriya Swayamsevak Sangh (have) never accepted the constitution and the citizenship of this country and they have the leverage now and the numbers to effectively destroy India's constitution, recreating India according to their imagination as a Hindu state."

India's northeast is home to more than 200 distinct indigenous minority groups. Both Assam and Tripura share a border with Bangladesh and some see the arrival of foreigners as a cultural threat regardless of religion -- for others, anti-immigrant sentiment remains closely tied to religious divisions.

Images from the protests show crowds chanting slogans and holding signs that read, "We are Assamese and proud" and "Tripura is not the dumping ground of illegal migrants."

"The northeast is (like) a separate country, it has so many races, religious groups, cultures, around (200) ethnic groups and we are still grappling to live together here," said Patricia Mukhim, a writer and editor at Shillong Times, the region's oldest English-language daily.

"We fear that we will become a demographic minority" if large numbers of Hindus are granted citizenship, she added. "All of us are very wary about that and then there is the case of that there are not enough jobs to go by, enough living space even."