The attacks followed a two-day lull in the state which earlier this week saw 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 Saturday's attack.
"Around 8:00am today, 15 Bihari labourers working in a brick kiln were shot dead by suspected militants in Bordubi area in Tinsukia district," B M Mazumdar, Assam's interior secretary, said. Tinsukia is about 500km east of Guwahati, the state's main city.
Earlier this week, several local organisations, among them
a key separatist guerrilla group, gave migrants from Bihar a
deadline of seven days to leave Assam.
Following the warning, thousands of Biharis fled Assam, some leaving behind their possessions. "We want to leave this place at the earliest. Our lives are at risk," said Raghu Narain, a Bihari labourer, waiting at Guwahati's railway station with his wife and three children.
"We want to leave this place at the earliest. Our lives are at risk"
"Most of them (Biharis) are travelling without tickets as they fled leaving behind whatever they had in their houses and they have no money," said Ashim Dey, a railway ticket collector.
The trouble in the state began after Assamese train travellers were attacked in Bihar last week, following reports early this month of assaults on some Bihari students who came to Assam to do tests for railway jobs.
Assamese students feared Biharis might corner the railway jobs that were available.