Papua New Guinea Prime Minister James Marape has threatened the strongest measures against "gun-toting criminals" after more than 20 people, including pregnant women and children, were killed in tribal violence in the western highlands.
The killing of 16 people on Monday in the village of Karida in the remote province of Hela were probably retaliation for an earlier attack that left around seven dead, Hela Governor Philip Undialu told the ABC.
"This has escalated into the massacre of innocent women and kids," he said.
The Post-Courier newspaper, based in the South Pacific island nation's capital Port Moresby, reported as many as 24 people were killed in the villages of Karida and Peta since Saturday.
Six people had been ambushed and killed near Peta on Saturday, Hela Police Chief Inspector Teddy Augwi told the newspaper.
The victims' relatives retaliated with rifles the next day, killing between 16 and 18 people at Karida, including pregnant women, he said.
"This is not a tribal fight where the opposing villagers face each other on field," Augwi told the newspaper.
"This is a fight in guerrilla warfare, meaning they play hide-and-seek and ambush their enemies."
Many villagers had fled the violence, Hela Administrator William Bando told the newspaper.
Tribal violence is common in Papua New Guinea's interior, where villagers avenge relatives in retaliation known as payback.
Health Department worker Philip Pimua, who visited the scene, told the ABC he believed eight of those killed were aged between one and 15, and that two of the women were pregnant.
Prime Minister Marape responded to the tragedies by saying on social media: "Today is one of the saddest days of my life."
He said many of the victims lived in his electorate and he blamed a police shortage in Hela for the lawlessness.
"How can a province of 400,000 people function with policing law and order with under 60 policemen, and occasional operational military and police that does no more then (sic) band aid maintenance?" Marape wrote.
Australian Foreign Minister Marise Payne condemned the violence and extended her condolences to the victims' families.
"The events in Papua New Guinea that have resulted in this massacre are an absolute tragedy and my thoughts and sympathies are with the families of those who have been so appallingly killed," she said in London.
"I know Prime Minister Marape has indicated that he will take every step he can to ensure that this sort of violence does not continue in Papua New Guinea and that those perpetrators are brought to appropriate justice."
Ahmad Hallak, head of mission for Red Cross in PNG, said he was concerned women and children had been killed, and urged restraint on all sides.
He said a Red Cross team would visit the area to assess the humanitarian consequences of the fighting before deciding on a response.
