The four were following the return of OPM co-founder Nicholas Jouwe to Indonesia after more than 40 years in exile in The Netherlands, Danto said, and are being held in immigration detention.

"Nicholas Jouwe's group had already left the area in the morning but they also covered the rally, despite not having permits," Danto said.

Local immigration official Raden Hendiartono said authorities had not yet decided whether to charge or deport the two male and two female journalists.

Around 1,000 protesters converged on the provincial parliament amid a tight police presence to call for a boycott of national legislative elections on April 9 and a referendum for independence in the resource-rich region.

The protesters chanted "Free Papua" and "Boycott the election" as they marched through the Papuan provincial capital carrying banners calling for an end to Jakarta's heavy-handed military presence in the region.

The 85-year-old Jouwe arrived in Indonesia last week, calling for peace between the Indonesian government and Papuans during a meeting with Welfare Minister Aburizal Bakrie.

Papua, which sits on the western end of New Guinea island, was formally incorporated into Indonesia after a 1969 UN-backed vote by tribal elders widely seen as a sham.

The government heavily restricts access to the region by foreign journalists.