Some 2,000 Indonesian police and troops have been sent to a district in Central Sulawesi province to prevent a major flare-up of Muslim-Christian violence, a police officer has said.
A government minister said separately the attack on four villages on Sunday, which killed eight people, mostly Christians, may have been timed to coincide with the first anniversary of the Bali bombings.
Witnesses have reported that the attackers wore masks, said Poso district deputy police chief Rudy Trenggono.
But he denied reports that telephone connections had been cut before the attack and that the attackers had planted nails near the villages to slow police movements.
National police said a man, who was injured when the bomb he was making exploded prematurely, has been arrested in Poso, where an estimated 1,000 people died in Muslim-Christian battles earlier this decade.
They said there was no evidence yet that the man was linked to Sunday's attack.
"His identity has not been clearly established," national police spokesman Brigadier General Sunarko Danu Ardanto told a press conference.
"He was assembling a home-made bomb, which exploded and injured him."
In a clash last Thursday, two people were killed and three wounded when a mob raided a mainly Christian village, near Poso, and burned homes.
The military has provided vehicles to take police personnel to troubled areas.
Top security minister Susilo Bambang Yudhoyono said he and other officials from the military and the national intelligence agency would fly to Poso on Tuesday to assess the situation and hold talks with local religious leaders.
He and other top officials have said outsiders rather than locals may have been involved.
Muslim militants from outside the province travelled to Poso to join in the fighting, which began in 2000, and which largely ended in December 2001 with a government-brokered peace pact.
The Al Qaeda-linked Jemaah Islamiah (JI) terror group, blamed for the Bali bombings and other blasts, has eyed Poso as a potential training ground, according to a report by the International Crisis Group of political analysts.
Twelve JI members and associates were arrested in the Central Sulawesi capital of Palu in April.
Outbreaks of violence in the province in mid-2003 "may be a signal of renewed activity by jihadists [holy warriors]," the group said in a recent report.
Top welfare minister Yusuf Kalla, who negotiated the peace deal, said on Monday the recent attacks were not carried by people involved in the old conflict.
He said the killings may have be carried out by sympathisers of Muslim militants convicted of last year's Bali bombings and of the bombing at a McDonald's restaurant at Makassar in neighboring South Sulawesi province.
"There are those who believe it is connected to the verdicts in the Makassar bombings and [the attacks] were at the same time of the one-year commemoration of the Bali bombings. Indeed there are coincidences," Mr Kalla said, quoted by Detikcom online news service.
More than 5,000 people also died in three years of Muslim-Christian clashes in the Maluku islands.
Muslim militants also travelled there, without interference from sections of the military, to help fight Christians.
More than 80 per cent of Indonesia's 212 million people are Muslims. But in some eastern regions, including the Malukus and Poso, Christians make up roughly half the population.