A teenager was killed and four other people were wounded when a bomb exploded outside their bus in the troubled Poso district of Central Sulawesi, according to police.

It is the latest challenge to a peace deal signed between Muslims and Christians in the area last December.

The explosion happened Friday when the bus driver's assistant, or conductor, got out of the bus to examine a bag found on the road in front of them, a police officer in Poso town told AFP Saturday. He said the wounded passengers and a 17-year-old girl who died had got out of the bus with the conductor.

He said they were travelling from the provincial capital of Palu to Tentena, a predominantly Christian town where the wounded are being treated at hospital.

"The hand of one victim was severed," the officer said.

Reports said the explosion happened about four kilometres (2.6 miles) from Poso.

The police officer could not say whether anybody has been arrested or what type of explosive material caused the blast.

"This is still being investigated," he said.

In June, four people died and 17 were wounded when a bomb ripped through a crowded bus near Poso.

An estimated 500 to 1,000 people were killed and tens of thousands made homeless during two years of intermittent Muslim-Christian fighting in the Poso area which broke out in 2000. A government-brokered peace deal in December brought a shaky peace to the region.

Another peace pact, also brokered by Jakarta, was reached in February between Muslims and Christians in the Maluku islands to the east of Sulawesi.

That agreement has also been threatened by bombings and other acts of violence.