As many as 15 people are feared to have been killed in a firefight between Indonesian soldiers and Papuan independence fighters, adding to more than two dozen deaths in the simmering conflict since November.

Indonesia’s military said three of its soldiers, and seven to 10 independence fighters, died on Thursday when a force of 50 to 70 rebels carrying firearms as well as spears and arrows attacked a group of 25 soldiers in a battle lasting several hours.

Sebby Sambom, a spokesman for the West Papua National Liberation Army, said five soldiers were killed and admitted no deaths for the Papuans. Both sides claimed to have captured weapons.

There has been no independent confirmation of the number of deaths, which is notoriously difficult in the region. Muhammad Aidi, the military spokesman for Indonesia’s easternmost Papua region, said the body of only one rebel fighter was found.

Aidi claimed the soldiers had arrived in the area to guard work on the trans Papua highway and the attack was unprovoked. According to Sambom, the soldiers had burned traditional dwellings and interrogated villagers.

Two helicopters sent to take the bodies of the three killed soldiers to the mining town of Timika were shot at but eventually landed after Indonesian forces returned fire, Aidi said.

The highlands district was the location of a December attack by Papuan fighters on workers at a construction site for the trans Papua highway that killed 19. Large numbers of people have been displaced by military and police security operations since the attack.

At least 31 people have died since early November in an apparent escalation of attacks by the West Papua National Liberation Army. The figure doesn’t include unconfirmed civilian deaths that Papuan activists say resulted from security operations.

An insurgency has simmered in Papua, which makes up the western half of the island of New Guinea, since the early 1960s when Indonesia annexed the Dutch-controlled territory.

Discrimination against indigenous Papuans and abuses by Indonesian police and military have drawn renewed attention globally as Indonesia campaigns for membership in the UN’s human rights watchdog.

The exiled leader of the Papuan independence movement, Benny Wenda, in January presented a 1.8m-signature petition calling for self-determination to the UN human rights chief in Geneva.