What happened?

Details are still emerging but according to eyewitnesses and local media, six people returning from a ceremony were ambushed and killed on July 6.

The next day gunmen entered Karida village in central Hela province and killed 18 people as well as two unborn children, shooting and hacking them to death.

Graphic images of the aftermath showed corpses bundled up in mosquito nets and small children with severe head wounds.

Who did it?

Police are investigating. But Prime Minister James Marape -- who comes from the area -- has blamed "Haguai, Liwi and OKiru gunmen" referring to three related warlords who have been fighting the Tagali tribe.

While the violence may cut along clan lines, it is unclear who the perpetrators are.

Highlanders say more and more outsiders are now involved in violent incidents -- including roving mercenaries and arms dealers willing to work for cash, pigs or the kidnap of women.

Why are they fighting?

Papua New Guinea is incredibly diverse, with over 800 languages, strong tribal identities and a central government that is often secondary to local courts and customs. The population has more than doubled in the last half-century, intensifying competition for land and resources.

The latest violence has been linked to control of nearby Mount Kare, believed to hold high-grade gold deposits.

Is this violence normal?

Death tolls are hard to come by, but tribal fights were reported long before Westerners first visited the highlands in the 1930s.

Some elderly highlanders speak of taking part in pitched battles with spears, arrows and axes within their lifetimes.

Those scenes are now rarer, but spasms of violence still occur and there is some evidence that the clashes may be getting more deadly.

There has been an influx of American M16s, AR-15s and Belgian FN rifles.

Papua New Guinean military intelligence say the weapons may come from nearby Bougainville Island -- where a civil war raged until 1998 -- or from across the porous Indonesian border, or even from within the security services themselves.

Where is this taking place?

The latest attack was in Karida village in Hela province, part of the central highlands region.

The area is extremely rugged, with dense vegetation and few roads or navigable rivers.

According to the International Red Cross, fighting kills dozens and displaces thousands every year.

Papua New Guinea has high crime rates but mistrust in the police is rife. Many people turn to private security firms before the police, especially in the capital Port Moresby -- which is among the most dangerous cities in the world.