Police in Papua have defended the fatal shooting of two pro-Papuan independence activists on Wednesday, saying that the pair tried to assault police officers as hundreds protested on the 50th anniversary of Indonesia's annexation of Papua.

"The shooting was according to procedure," Papua Police spokesman Sr. Comr. I Gede Sumerta Jaya said on Saturday.

Sumerta said that police in Sorong, West Papua, acted in self-defense after they were assaulted with sharp weapons as they guarded the demonstration.

UN High Commissioner for Human Rights Navi Pillay on Friday expressed serious concerns over the heavy-handed crackdown on demonstrations across Papua during the anniversary.

At least 20 protesters were arrested in Biak and Timika cities on Wednesday.

Pillay added that there was a need for coherent policies and actions to address the underlying concerns and grievances of the local population in Papua.