Thirteen people including five women were killed in violence during the third and final phase of panchayat polls in lower Assam's Goalpara district, 250 km west of Guwahati, on Tuesday.
The Rabhas had opposed the panchayat polls in the Rabha Hasong Autonomous Council Areas, whose jurisdiction extends up to Rani area in adjoining Kamrup district, but others voted.
The Rabhas do not follow the panchayati raj system and have been demanding their own autonomous council on the lines of the Bodoland Territorial Council.
The Rabha Hasong Joint Action Committee had called a 36-hour 'janata curfew' from 7am on Monday. Violence was also reported from southern parts of Kamrup, forcing the government to seek the army's help.
"The army has been deployed in Goalpara district. Curfew has been clamped in several places," said GD Tripathy, secretary of the state home department.
"The police and paramilitary personnel were forced to open fire after mobs attacked them and targeted polling stations," he added.
Four CRPF personnel and three police officials were injured in the violence. The All Rabha Student Union claimed 16 Rabhas were killed in the police firing.
Amid the violence in Goalpara, three polling officials were reported missing from Krishnai area.
State election commissioner Biren Dutta said, "We did not anticipate such large-scale violence in Rabha Hasong areas. Our assessment went wrong."
CM Tarun Gogoi announced Rs. 5 lakh compensation for the next of kin of those killed in the police firing. He said nobody could stop the polling because it was a democratic process.