More than 20 people -- mostly women and children -- have been killed in days of tribal violence in Papua New Guinea, according to officials.

Papua New Guinea Acting Police Commissioner Francis Tokura said Wednesday that 16 women and children were killed this week by assailants armed with rifles in the village of Karida

The attack on Monday was believed to have been in retaliation for an earlier attack on a different village, Peta, that left 7 dead, Sky News reported.

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"This has escalated into the massacre of innocent women and kids," said Philip Undialu, the governor of the remote highland province of Hela.

Tokura told the Associated Press that because two of the victims in Karida were pregnant, police put the death toll at 18.

In the wake of the attacks, 20 police officers and 10 soldiers were sent to Hela to "stop any further violence and capture the killers."

"This is a tragedy. It is an unbelievable, unthinkable and atrocious criminal act that must be dealt with swiftly and severely," Tokura said in a statement.

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Papua New Guinea Prime Minister James Marape posted a statement to Facebook after the killings, saying "today is one of the saddest day of my life."

He also 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 band aid maintenance," he wrote. "To all who have guns and kill and hide behind the mask of community, learn from what I will do to criminals who killed innocent people, I am not afraid to use strongest measures in law on you."

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Tribal violence is common in Papua New Guinea's interior, where villagers avenge relatives in retaliation known as payback, according to the AP.

Hela official Rex Humbi told the AP the latest violence was part of a tribal war that had been waged for more than 15 years.

"The people that got killed were innocent women and children," he said. "The police do go and investigate. They have the authority, of course, but don't have the firepower" to bring the killers to justice.

The killers were possessed by Satan and "feed on the soul, or the spirits, of the innocents that have been lost," Humbi said.

The Associated Press contributed to this report