The army was called out and an indefinite curfew was imposed on Friday night in Assam after a huge mob set ablaze a police station and pelted stones at passing vehicles and security personnel.
The attack was on the Kakopathar police station in Assam's Tinsukia district.
Eyewitnesses said three villagers were killed in the police firing while a Central Reserve Police Force jawan was killed in the stoning by the mob.
The mob was protesting against the death of suspected ULFA linkman Ajit Mahanta allegedly in army custody on Sunday.
Official sources confirmed that there were casualties in the firing but declined to state the exact number of people killed or injured.
Residents of Kakopathar, from where Mahanta hailed, and nearby villages have blocked National Highway 52 since Monday.
The villagers, who claimed Mahanta was an innocent man, have also dug up the highway that links Lohit district of Arunachal Pradesh with the rest of the country.
Tinsukia Deputy Commissioner Gautam Ganguly told PTI that the army has been called in to assist the civil administration and indefinite curfew imposed in Kakopathar.
The district administration, he said, was considering the possibility of imposing curfew in the entire Tinsukia district as there were reports that the villagers were regrouping to launch further attacks on security personnel.
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