Thousands of people in Indonesia's far-eastern Papua region protested Tuesday for independence, following political violence that killed 21 people.

Demonstrators marched past heavily armed anti-riot police in cities in Papua, including the provincial capital, Jayapura. The protesters demanded a referendum on independence from Indonesia.

Those rallying in Jayapura tried to reach the provincial parliament building, but were blocked by police.

The protests followed the death of four people in a pre-dawn ambush by unknown gunmen Monday near Jayapura. A separatist flag was found at the scene, but the rebel Free Papua Movement has denied involvement. Elements of security forces also have been suspected of staging the attack.

On Sunday, 17 people died in clashes in the Papua region between supporters of rival political candidates. Media reports at the time said fighting broke out when the local election commission rejected the registration of a candidate running for district chief.

Indonesia's Papua province is located on the western half of the island of New Guinea. The region has been the scene of a low-level separatist insurgency for decades.