More than two dozen people were killed in a gunfight on Sunday in the remote highlands of Papua New Guinea, where deadly violence between more than a dozen tribal groups has been escalating. The precise cause of the latest episode remained unclear.

“What I’ve been briefed on thus far is that a situation occurred in the early hours of yesterday, Sunday the 18th, in Enga where a gun battle between warring tribes ensued,” David Manning, the police chief of Papua New Guinea, told reporters, referring the Enga Province.

Officials initially reported a death toll of more than 50, but that number was revised down to 26, according to the Australian Broadcasting Corporation.

“These tribesmen have been killed all over the countryside, all over the bush,” George Kakas, the Royal Papua New Guinea Constabulary acting superintendent, told the broadcaster. “Police and defense forces have had to go in to do their best to quell the situation at their own risk.” The police did not immediately respond to a request for comment.

Bodies were found across a field, along roads and near a river, Mr. Kakas said. Video footage and photos shared on social media, whose authenticity could not immediately be confirmed, showed dozens of bodies piled onto the back of an open truck.

The police said as many as 17 tribes were involved in the clashes. A mobile police squad has been sent to the area, Mr. Manning said.

Only men are believed to have been killed, and there is some evidence that some of the fighters may have been hired for their services, said Serhan Aktoprak, the local head of the International Organization for Migration, a United Nations agency.

“The actual fighters are reported to be hired men from different parts of the province,” he said. “There are mercenaries who offer their services, using sophisticated firearms in exchange for money. For them, it doesn’t matter whom they serve, as long as they are paid.”

Estimates vary, but at least 10 million people are believed to live in Papua New Guinea, which is mostly rural and larger than California, with roughly 85 percent of the population living outside of urban centers. It is rich with mineral resources but remains impoverished. Culturally, it is extremely diverse; more than 300 tribes are spread across the country and the bordering Indonesian regions of Papua and West Papua, according to Survival, a group that advocates for Indigenous rights. More than 800 languages are spoken in Papua New Guinea.

“From the outside, it will look like they’re one country,” Elizabeth Koppel, a researcher at the Papua New Guinean National Research Institute, said during a panel discussion organized by the United States Institute of Peace about tribal violence in October. “But we really struggle with trying to live with each other, understand each other, given all the different diversities.”

Tensions have for several years been rising in the highlands, including Enga Province, where the recent deaths occurred. “This sort of situation has been just becoming increasingly more severe for many years now,” said Michael Main, a researcher at the Australian National University. He added: “It’s been going on for so long that you have an entire generation that’s growing up deeply, deeply traumatized. This level of violence has become normalized.”

Limited water and other resources, as well as disagreements over private land, have long set off tensions, said Mr. Aktoprak. “The main factors that lead to horrifying incidents such as this actually have been around for generations,” he said.

The death toll has been rising in recent years as tribespeople have moved from using traditional weapons to high-powered firearms including semiautomatic guns that are mostly brought in from overseas. “Previously, tribal fighting would involve spears and bows and arrows, leading to deaths but less casualties,” said Peter Murorera, also of the United Nations’ migration agency.

The Papua New Guinean defense force “acknowledges that it’s basically outgunned,” Dr. Main said.

The issues in the highlands date back many years and are highly localized and often very personal, often relating to longstanding grievances over land or politics. That is complicated further by a young population that is undereducated and underemployed, with young people denied an education because they are forced to flee the fighting, in turn resulting in mass displacement of thousands of individuals.

“You’ve got people fighting for economic resources, whether it’s ownership of land on which a development project is located, or coffee plantations,” Dr. Kopel said in her remarks last year. She added: “The law doesn’t intervene quickly enough, then people resort to taking the law into their own hands, and sometimes fights are instigated by law enforcement agencies.”

At least 150 people were killed in clashes in 2023, and last year, the authorities put Enga Province on a three-month lockdown to contain the unrest.

Peter Ipatas, Enga’s governor, called on Australia last year to help security forces in Papua New Guinea contain the violence. “We do not have the capacity to fix this,” he told the newspaper The Australian.

“The level of violence and, basically, the harm that is done to people is going out of control,” said Mr. Aktoprak of the U.N. “It is something they cannot themselves solve through the traditional and customary means of intervention and mediating efforts.”

Last year, Australia agreed to expand support and training for Papua New Guinea’s police under a security agreement. Speaking to the ABC on Monday, Prime Minister Anthony Albanese of Australia hinted that more assistance to Papua New Guinea could be forthcoming.

“We remain available to provide whatever support we can in a practical way to help our friends in PNG,” he said.