Indian police recovered 12 bodies from rice fields and roadsides in the remote state of Assam on Wednesday as the death toll from ethnic violence rose to 38 after four days of bloody clashes.

At least 170,000 villagers have fled their homes to seek shelter in relief camps, government buildings and schools to escape the unrest, which has raged since Friday with scores of homes burned down by rioters.

Military reinforcements were called in to try to quell the fighting between indigenous Bodo tribes and Muslim settlers who have competed for years in long-standing territorial disputes.

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"It appears all these 12 people were killed in overnight attacks," said Tarun Gogoi, the chief minister of Assam, a oil and tea-rich state in the northeast of India bordering on Bhutan and Bangladesh.

"The situation is tense," Mr. Gogoi told AFP, adding that there had been a "massive deployment of army, police, and paramilitary troopers".

Northeast India, which is linked to the rest of the country by a narrow land bridge, has seen decades of friction among ethnic and separatist groups, though some rebel movements have recently started peace talks with the government.

News channels broadcast pictures of homes that had been set ablaze by rioters, and of women and children gathered in the government-run camps where food was handed out and soldiers were on duty to provide protection.

Hagrama Mohilary, chief of the Bodoland Territorial Council, a local government body, told AFP by telephone that an estimated 170,000 people are sheltered in relief camps.

Mr. Mohilary said the latest victims had been killed with crude weapons such as heavy sticks, and their bodies left at separate sites in fields and besides roads.

"Incidents of arson and violence were reported from several places," he said.

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Police have issued shoot-on-sight orders after rioters burnt shops and houses and attacked rival gangs. The orders mean that mobs can be shot without warning.

Four rioters attempting to burn down properties were killed by security forces on Tuesday.

"We have lost everything in the violence. Our houses have all been razed to ground with mobs setting ablaze our properties," Rabiul Islam, a villager in Kokrajhar district, told local television at one camp.

"We don't know how long we have to stay in the relief camp. We left everything behind and simply ran for our lives," said Ronila Brahma, a mother of two children, who had fled her home carrying just a few belongings.

Most rail services in the region were disrupted after some trains were ambushed by crowds pelting stones, and many roads into the region were closed.

"We have cancelled all incoming and outbound trains in view of the violent situation," railway spokesman T. Hajong said.

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Prime Minister Manmohan Singh on Tuesday issued a statement calling for Assam authorities to do "everything possible to control the situation" and for emergency relief supplies to be rushed to those in need.

A team of senior Indian home ministry officials has also arrived in the state to oversee the security plan.

The Press Trust of India news agency has reported that the fighting started when two Muslim student leaders were shot and seriously injured in Kokrajhar, leading to revenge strikes on Bodo groups.