More than two dozen people were killed in a gunfight Sunday in the remote highlands of Papua New Guinea, where deadly violence between more than a dozen tribal groups has been escalating. The cause of the latest episode was 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 gunbattle between warring tribes ensued,” David Manning, the police chief of Papua New Guinea, told reporters, referring to 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 Corp.

“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.” Ppolice did not immediately respond to a request for comment.

Bodies were found across a field, along roads and near a river, 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.

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

“From the outside, it will look like they’re one country,” Elizabeth Kopel, a researcher at the Papua New Guinea 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.”

This article originally appeared in The New York Times.