At least nine civilians were shot dead and 23 wounded when security forces opened fire on a crowd of demonstrators. Police said they were aiming at separatists who were leading the protests.

The BBC's Simon Ingram: "Separatist tensions are again coming to the boil"

The clashes followed a military operation against suspected members of the separatist Free Aceh Movement, which was blamed last week for the murder of at least seven soldiers.

Angered by the arrests, a crowd attacked a police post and government buildings. Security forces opened fire to disperse the rioters, reportedly using live ammunition.

The BBC South-East Asia Correspondent, Simon Ingram, says the sudden escalation of violence in Aceh suggests separatist tensions are again coming to the boil, despite attempts by the government to appease popular feeling by withdrawing combat troops from the province and offering an apology for the often brutal suppression carried out by the military there.

Circle of violence

Clearing up after Saturday's bomb attack in Jakarta

But the violence in Aceh is only part of a broader picture of unrest sweeping many parts of Indonesia.

On Saturday, a police station and shops were set alight in the second city of Surabaya.

The crowd had been angered by rumours that a suspected thief had died in police custody.

In west Java, two factories were attacked by villagers angered by the environment damage they caused. And in Sulawesi, angry Muslims ransacked a shop whose Chinese owner was suspected of misusing a prayer mat.

Indonesia has been rocked by a series of violent protests as Asia's economic crisis has exacerbated social and ethnic tensions. As many as one third of the country's 200 million people have now fallen below the poverty line.

Popular suspicions

Correspondents say many Indonesians have become suspicious of the authorities - particularly the military, which includes the police force - because of its former role as backbone of former President Suharto's regime.

Mr Suharto's successor and former protege, BJ Habibie, has promised national elections in June, but the protests have continued with many people complaining he is not moving fast enough on political reforms and weeding out official corruption.