Jakarta – Five people have been detained following a powerful blast this week that killed four people and wounded dozens of others in Indonesia's eastern city of Ambon, reports said Friday.

"We have detained five residents for questioning," Maluku police chief Brigadier General Sunarko Danu Ardianto said, according to Media Indonesia daily. Sunarko said early investigations pointed to three people not in custody as possible masterminds of the bombing on Wednesday. Officers at Maluku police headquarters in Ambon refused to confirm any arrests.

The blast killed four people and wounded 58. An angry mob set fire to the governor's office following the explosion.

A government-brokered peace pact signed in February by Muslim and Christian delegates ended three years of sectarian clashes in Ambon and the rest of the Malukus in which some 5,000 people were killed and half a million driven from their homes.

But some parties oppose the pact, saying the delegates were not representative of society. Among the opponents are the militant Muslim Laskar Jihad and a Christian separatist group.

A local reporter said several explosions and sounds of gunfire were heard on Thursday night in Ambon, the capital of Maluku province, but there were no reports of casualties.

Muslims and Christians had begun mingling freely in Ambon following the February 12 agreement, which Jakarta hailed as another landmark in efforts to end sectarian and communal unrest in the huge archipelago. A similar pact in December ended Muslim-Christian fighting in the Poso region of Sulawesi.

Ambon and the rest of the Maluku islands had been relatively peaceful since the peace pact in February. More than 80 percent of Indonesia's 214 million people are Muslims but in some eastern regions, including the Malukus, Christians make up about half the population.