Two bomb blasts have ripped through a crowded market in a Christian town in eastern Indonesia, killing at least 21 people and injuring 40, Aljazeera reported.

Police said the attacks occurred on Saturday in the lakeside town of Tentena on the eastern island of Sulawesi, part of an area where three years of Muslim-Christian clashes killed 2000 people until a peace deal was agreed in late 2001, Reuters news agency reported.

Periodic unrest has flared since, but Saturday morning's attack is among the worst and is likely to raise fears that sectarian bloodshed could break out again in the region.

"The first bomb exploded in front of the Tentena market, the second explosion took place about 15 minutes later," Sukirno, deputy police chief for Central Sulawesi province, said. 

Suhaib Jasim, Aljazeera's correspondent in Indonesia, said the first bomb exploded at 8am and the second at 8.15am, local time. A church official said 21 people were killed and 40 injured, Jasim said.

Investigation 

The El Shinta radio station said the second explosion was the stronger of the two.

"The market was packed. It lies in the heart of the town. Victims have been taken to hospital," one unidentified caller told Indonesia's leading news radio station.

The market is near churches and a Christian school, Jasim said.

Tentena residents are questioning the motives behind the explosion, Jasim said, after a recent show of peace between religious leaders in the region. Several weeks ago, the Islamic al-Mujahidin Front's leader and the head of churches in the area were seen embracing each other.

Christians make up 70% of the town's population, but Muslims are a majority in surrounding areas, Jasim said.

Sulawesi conflict

Much of the past Sulawesi violence focused on the town of Poso, which is about 1500km northeast of Jakarta.

Picturesque Tentena, famous for its churches and surrounded by clove-covered hills, is 40km south of Poso.

The Sulawesi conflict drew fighters from groups such as the Jemaah Islamiah, a Southeast Asian network blamed for numerous bomb attacks across Indonesia.

About 85% of Indonesia's 220 million people are Muslim. But in some eastern parts, Christian and Muslim populations are about equal in size.

Heightened security

The two explosions follow heightened warnings from Western governments about terrorist attacks in the world's most populous Muslim nation.

PHOTO CAPTION

Indonesian forces in Palu, Central Sulawesi during a government security crackdown to end deadly violence between Christans and Muslims in 2001. (AFP)