Soldiers patrolled India?s northeastern state of Assam yesterday after an orgy of killing, looting and arson targeted at settlers from a neighbouring state. Police said thousands of people had sought shelter in police stations across Assam after hundreds of homes were set alight during three days of violence that have killed at least 15 people.

Several local groups ordered migrants from Bihar state to leave Assam within seven days and one separatist group vowed to kill them. ?You can say many parts of Assam are on fire?, a senior police officer said.

Mobs targeted Biharis, looting their houses, assaulting those inside and setting the wood and tin structures on fire using petrol and kerosene, he said.

In one attack, four women and two children belonging to one family were hacked to death yesterday and their home set alight in Dibrugarh town, about 250 km (155 miles) from Guwahati, police said.

The killing spree began on Monday, driven by anger over an attack on Assamese train travellers in Bihar last week, triggered by a competition for jobs in the oil and tea-rich Assam.

Police said an indefinite curfew had been imposed in Tinsukia, one of the two worst affected districts along with neighbouring Dibrugarh.

?The army has been called out across the state to control the situation as we are facing a shortage of federal police forces?, Assam?s Chief Minister,Tarun Gogoi, told a news conference. He said 15 people had died since Monday.

He said 500 people had been arrested on charges of being involved in arson and rioting and the state, which is also torn by a 25-year insurgency, had sought more federal police forces.

A separatist group ordered Biharis to leave or be killed. ?All Biharis staying in the state should immediately move out of Assam, or face bullets,? said Paresh Barua, commander-in-chief of the United Liberation Front of Asom (ULFA).

Suspected ULFA rebels sprayed automatic weapons fire at a group of Bihari migrants watching a local cricket match near Guwahati on Tuesday night, killing four and wounding seven, police said.

The ULFA, which is fighting for an independent nation of Assam, accuses New Delhi of plundering the state?s resources and neglecting its development.

Though thousands of Biharis have settled in Assam over the years, there have been no reports of tension between the communities until now.

The trigger is believed to have been an attack on Assamese train travellers in Bihar last week following reports early this month of assaults on Bihari students who came to Assam to do tests for railway jobs.

Assamese students feared Biharis might corner the railway jobs that were available.

Biswajyoti Das