The crowd had gathered to listen to a speech by the separatist Free Aceh movement in the town of Idi Cut.

A spokesman for a human rights group said the incident began when police beat street vendors to try and clear them from a path.

"The people got angry and that's when the police started to shoot," the spokesman said. "The situation is still tense."

Police have acknowledged that two people died from gunshot wounds, and say they arrested 51 people who were attending an unauthorised gathering.

A lawyer for the Iskandar Muda Legal AId Foundation said residents identified 12 bodies, but added there was another which had not been indentified.

Separatist tensions have simmered for years in Aceh, a staunchly Muslim province at the north of the island of Sumatra.

Brutal military repression has exacerbated resentment towards the Jakarta government. Last month an army officer was jailed for torturing civilians during a raid on separatist leaders.

Last year Indonesia announced a troop withdrawal from the province, but cancelled it following riots.

Early this year 11 people died when police opened fire on a crowd which attacked government buildings near the town of Lhokseumawe.

Religious fighting

In eastern Indonesia, clashes between Muslims and Christians in the island of Ambon resumed on Wednesday after leaving at least 95 people dead last month.

On Thursday, over 1,000 villagers were reported to have fled a fire which engulfed their homes in Seram island, north of Ambon.

The fire broke out during a fight between two youths, and villagers panicked as the blaze spread, an Indonesian newspaper reported.