"Indefinite curfew had to be implemented in Imphal and in some other districts," L. Kailun, a senior police official based in the state capital, told Reuters.
He added that the situation was "extremely tense" after armed mobs vandalised an office of the ruling political party and hurled petrol bombs at two police sites.
More than half the state's population of 3.2 million belongs to the Meitei community, while the Kuki community, who make up about 43%, live mostly in the hills.
Protests re-ignited over the alleged kidnapping and killing of two students of the Meitei community who had gone missing in July, after their bodies were found this week.
Leaders of the opposition Congress party have accused the Modi government of failing to control the violence in a state governed by his nationalist party.
Persons:
Stringer, Biren Singh, Narendra Modi's, Kuki, Modi, Rupam Jain, Clarence Fernandez
Organizations:
Riot, REUTERS, Reuters, Mobile, Thomson
Locations:
Imphal, Manipur, India, DELHI, Myanmar, Kuki