A church and a UN office were torched and at least four people killed on Sunday as Muslim and Christian residents of the eastern Indonesia city of Ambon fought pitched street battles, witnesses and police said.
Dozens of people were also injured as mobs rampaged through a majority Christian area of the provincial capital of the Moluccas province, witnesses said.
Gunfire and explosions could be heard in several parts of the city. It was not clear who was firing and the mobs were using mostly stones and knives.
"At the moment we know at least four people have been killed, but that toll could rise," Moluccas police chief Brigadier-General Bambang Sutrisno told Reuters. He did not say how the victims had died.
Thousands of people were killed in the Moluccas during nearly three years of sectarian conflict before a peace deal was agreed in early 2002. Civil emergency curbs were only lifted last year.
Sunday's clashes began after police arrested and then released a number of people for trying to raise the banned flag of a little known and mostly Christian rebel group, the South Moluccas Republic movement.
"There are at least 40 injured in some hospitals. We are still trying to control the situation." Jakarta-based El Shinta radio reported two people had been killed.
Novi Pinontuan, editor of the Suara Maluku newspaper in Ambon, told Reuters he had seen a church and a local U.N. coordinating office in flames and that hundreds of people were rampaging through parts of the city.
"The office and four U.N. cars were in flames," he said.
Caroline Tupamahu, the United Nations Development Program officer in charge in Ambon, said no staff had been injured and only two local security guards had been at the office.
A witness told Reuters he had seen at least one dead body and dozens of injured people in various Ambon hospitals.
Residents said police fired shots in the air in an effort to break up the clashes.
Some 85 percent of Indonesia's 220 million people are Muslim. In some eastern areas, however, the Christian and Muslim populations are about equal in size. (Additional reporting by Telly Nathalia in Jakarta)