Separatist rebels were holding four civilians hostage in the jungles of Indonesia's breakaway Papua region after they killed several construction workers in an ambush, authorities said Friday.

Tensions have been mounting between Indonesian security forces and guerrillas fighting a decades-long insurgency to win independence from the Southeast Asian nation.

Authorities said some 30 rebels opened fire Thursday on a group of Indonesian construction workers building new homes in the province's central Yahukimo regency, killing at least four people.

Rescue operations to find another four people being held hostage by the rebels are underway, according to the military and Papua police spokesman Ahmad Musthofa Kamal.

"Our team is on their way to the site," Kamal told AFP on Friday.

It was not clear if all of the hostages were construction workers.

A rebel spokesman could not be reached for comment and AFP was unable to independently verify the account.

Tensions in Papua have heated up since rebels executed Indonesia's top intelligence official in the region in April
Tensions in Papua have heated up since rebels executed Indonesia's top intelligence official in the region in April AFP / Sevianto Pakiding

Tensions in the conflict-wracked region have soared in recent months, punctuated by deadly clashes after rebels killed Indonesia's top intelligence chief in Papua in April.

Jakarta responded by formally designating Papuan separatists as "terrorists", sparking fears it could open the door to more violence and rights abuses.

Indonesia's counter-terrorism laws give authorities enhanced powers, including holding suspects for several weeks without formal charges.

The latest incident comes more than two years after Papuan rebels killed 17 construction workers at a remote jungle camp.

The massacre marked an escalation in decades of mostly sporadic skirmishes between poorly armed and disorganised guerrillas and an Indonesian military long accused of gross human rights abuses against civilians.

A former Dutch colony, mineral-rich Papua declared itself independent in 1961, but neighbouring Jakarta took control two years later promising an independence referendum.

The subsequent vote in favour of staying part of Indonesia was widely considered a sham.

Papua's Melanesian population shares few cultural connections with the rest of Indonesia.