Indonesian police say they suspect a gang of agitators behind a string of attacks across sectarian violence-hit eastern islands may be responsible for a weekend bombing that killed 21 people.

The police chief of Indonesia's Maluku island chain, the scene of frequent unrest between Christians and Muslims, said Saturday's blasts in the Sulawesi island town of Tentena appeared to match a pattern of attacks in his region.

"We indicate the possibility that they are part of the same group," Aditya Warman told reporters.

Warman refused to say whether the gang of three was linked to Islamic militants blamed for terrorist attacks in Indonesia including the Bali bombings, but added that at one incident they left a Koran and a flag bearing the word "mujahedin".

Detectives earlier said the Tentena attack bore hallmarks of Azahari Husin, a Malaysian fugitive wanted for alleged roles in the Bali strike and deadly explosions at a Jakarta hotel and the city's Australian embassy.

Warman said the three agitators were wanted in connection with six attacks between November 2004 and May 2004, including a "carefully planned" raid on an elite police unit on the Maluku island of West Seram.

They were also believed to have been involved in incidents including the abduction and murder of a Christian cleric and an attack on two Christian villages.

Like the Malukus, much of Sulawesi has been plagued by warring between Christians and Muslims. A year of open conflict claimed more than 1,000 lives in Sulawesi before a peace deal in 2001, but sporadic violence has continued.

Indonesian officials have said Saturday's attack could be an attempt by Islamic extremists to stir up fresh trouble. Others have said the attack was politically motivated to justify a stronger military presence in the region.

Warman said the latest information came from a purported member of the gang who was already in custody. The captive was from the Java island town of Solo, seen as the seat of Islamic extremism in Indonesia.

Meanwhile, detectives in Poso, close to Tentena, have been quizzing two convicts from the town's jail who, according to witnesses, were seen ahead of the explosions in the marketplace targeted by the bombers.

The head of Poso's prison was also being investigated after he was picked up in a car alongside the two armed convicts.

National police spokesman Aryanto Budiharjo said police were "conducting an intensive questioning of two people whose status are convicts".

Budiharjo said he doubted claims that Saturday's attack was a suicide bombing, although one of the victims was a man from outside the region whose name seemed to indicate he was a Muslim. "At the moment, I'm of the opinion that it was not a suicide bombing," he said.