At least seven people have been killed in the past week and hundreds of homes burnt down during clashes between armed Muslim groups and Christians.
Christian groups have accused Muslim paramilitaries of the Laskar Jihad organisation of recently entering the area and stirring up violence.
Laskar Jihad has been fighting Christians in the Molucca islands near Sulawesi since last year.
'Living in fear'
In the province of Sulawesi at least 1,000 people have been killed in religious fighting in the last two years. But until fresh violence broke out last week there had been a period of relative calm.
In the mainly Christian town of Tentena on Tuesday, people were reported to be getting their weapons ready for attacks by Muslims who have surrounded the village.
"People in Tentena and the surrounding areas are now living in fear of more violence," said a Catholic priest in the town, Jimmy Tumbelaka.
"There is no sense of security left."
In other parts of the region, Muslims have fled their homes fearing attacks by Christians, police said.
Ministerial visit
On Monday top security minister Susilo Bambang Yudhoyono said he was sending 2,600 extra troops to Poso, where police and soldiers are already patrolling towns and villages.
He plans to visit the area with military commander Admiral Widodo Adisutjipto and the newly-appointed police chief, General Da'i Bachtiar. Mr Yudhoyono said the government would then decide whether to declare martial law.
According to reports, armed Muslims burnt down six Christian villages last week, forcing about 13,000 people to flee. This could not be independently confirmed.
Police have reported no new clashes since early on Sunday.
Human rights activists have accused the government of not doing enough to end the bloodshed.
In the troubled province of Aceh, on the northern tip of Sumatra island, separatists on Tuesday marked the 25th anniversary of their struggle for independence.
Eyewitnesses in the provincial capital, Banda Aceh, said security forces tore down separatist flags but there were no reports of violence.
The rebel Free Aceh Movement (GAM) has been fighting for an independent homeland since the 1970s. More than 1,300 have been killed in separatist-related violence this year alone.