Eleven Bihari brick-kiln labourers were shot dead on Saturday by militants belonging to the United Liberation Front of Asom in Tinsukia district of Assam.
Another Bihari was killed in Kakopathar in Dibrugarh district in a group clash.
With the latest killings, the toll in the week-long anti-Bihari violence in the state has gone up to 46.
Tinsukia's Deputy Commissioner B N Das has been transferred and Superintendent of Police I K Gogoi placed under suspension, Home Commissioner and Secretary K D Tripathi said.
Inspector General of Police K N Sarma told PTI that a group of ULFA militants came to the brick kiln near Mahakali Tea Estate in Bordubi and opened indiscriminate fire.
There have been repeated clashes between Biharis and Assamese after some candidates from Bihar were prevented from appearing for a railway recruitment test in Assam.
The incident found its echo in Bihar where trains entering the state from the northeast were attacked.
Chief Minister Tarun Gogoi has called a high-level meeting with senior officials to review the situation.