The attack followed a two-day lull in Assam after widespread looting and killing of people from neighbouring Bihar state in a conflict triggered by a competition for jobs.
At least 34 settlers had been killed before today's attack, forcing the state to deploy the army to control the spree of violence that began last Monday.
Police blamed the attack on the outlawed United Liberation Front of Asom (ULFA), a powerful insurgent group fighting for an independent Assam nation.
The ULFA, blamed for most of the killings this week, has ordered Biharis in Assam to leave the state or face death.
The violence was triggered by attacks on Assamese train travellers in Bihar last week after reports of assaults on Bihari students who came to Assam to do tests for railway jobs.
Assamese students feared Biharis would snatch the prized jobs.
Thousands of Biharis have lived in Assam for years but there was no tension between the two communities in the past. Many settlers have fled the state after the bloody attacks.