Six Indonesian soldiers have been arrested after being accused of killing four indigenous Papuans and mutilating their bodies last week, authorities said on Tuesday.

The suspects pretended to be willing to sell weapons to lure the victims on August 22, the day the crime allegedly occurred, Papua provincial police director Faizal Ramadhani told AFP.

The victims were then dismembered, stuffed into sacks and thrown into a river outside of the city of Timika, according to a police report.

As of Monday, body parts belonging to three of the victims had been found, Ramadhani said, adding that authorities were continuing to look for the remains of the last victim.

The Papua police have also named four civilians as suspects in the case, three of whom were arrested over the weekend, Ramadhani said.

The civilian suspects said that the soldiers were "directly involved" in the killing and dismemberment of the victims, who are believed to be affiliated with rebel groups in the Nduga area, Ramadhani said.

Military investigators were questioning the six soldiers, who were named as suspects and arrested by the military police on Monday, military official Chandra W. Sukotjo said on Tuesday.

Teguh Muji Angkasa, a senior military officer in Papua, told reporters in Jayapura on Monday that the army was coordinating with the police on an investigation.

"We are committed to upholding the rule of law. We will hand out firm sanction if the soldiers are proven to be involved (in the crime)," Angkasa said.

Sebby Sambom, a spokesman of the West Papua National Liberation Army, the military wing of Papua's main separatist group, demanded that the Indonesian government sentence the perpetrators to death.

"This is a crime against humanity by the Indonesian government through its security forces," Sambom said in a statement, threatening to carry out a "retaliation operation" if his group's demand was ignored.

Indonesia maintains a heavy military presence in the resource-rich but underdeveloped Papua region, where the conflict with a rebel separatist insurgency has been claiming an increasing number of victims.

A former Dutch colony, Papua declared itself independent in 1961, but neighbouring Indonesia took control of the region two years later, with the promise of holding a referendum on independence.

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