Police blamed the attacks on the United Liberation Front of Asom (Ulfa), which has been fighting for the independence of Assamese people in an almost three-decade-long insurgency that has killed thousands.

Curfew was slapped across the state late Saturday, and was expected to be reviewed by security officials later Sunday. Federal troops have the authority to shoot anyone defying the order.

"We are going all out against the Ulfa," Tarun Gogoi, Assam's chief minister, told Reuters.

"Massive combing operations have started and additional troops are being rushed to the affected areas."

"The central government would send adequate reinforcement of paramilitary forces immediately to tackle the situation and ensure security of common people in Assam," India's junior home minister Sriprakash Jaiswal said.

The wave of violence started late on Friday with the gunning down of 48 labourers and traders. An explosion on Saturday killed seven people, including four policemen.

On Sunday, suspected rebels shot dead two supporters of the state's ruling Congress party after calling them out of their homes.

Security was tightened in areas adjoining the violence-hit eastern districts of Tinsukia, Dibrugarh, Golaghat and Sivasagar to prevent a spill-over of violence.

Most of the victims were migrant labourers from Bihar, who have been attacked in the past by rebels to gain the union government's attention, security official said.

Last week the Ulfa had warned non-Assamese businessmen and labourers of dire consequences if they continued to live in Assam, accusing New Delhi of flooding the state with outsiders to reduce the indigenous Assamese population to a minority.

"The Ulfa's only motive behind the killings was to create panic," Gogoi said.

"Orders have been given to military and police to intensify their battle against the Ulfa.

"There is no question of going soft on the militants."

Police said the violence was an attempt to intimidate people after an independent opinion poll by a peace group in nine districts of the oil- and tea-producing state showed 90 percent of respondents rejected the Ulfa's separatist demands.

Security analysts said that, with the attacks, the Ulfa had sent a message to New Delhi that it was still a force to reckon with and that decades of battle had not blunted it.

"The Ulfa wants to make it clear that government should not try to ignore it and also wants to prove that it still has the strength to strike at will," analyst Harekrishna Deka told Reuters.

The attacks came after officials had appealed to the rebels not to disrupt national games next month, as they have threatened to do.

Rebel attacks have increased since September after the Ulfa and New Delhi called off peace talks and government troops ended a truce.

Since then, the rebels have bombed crowded markets and railway stations, killing dozens of civilians in a conflict that began in 1979 and has killed more than 20,000 people.