The massacre took place in the province of Hela, a wild region in the west of the country, in a spasm of violence between rival tribes that lasted three days.
Mr Marape, who became leader in May, blamed a lack of police on the ground as a major problem in a region that has struggled with violence for years.
While it is not yet clear what the exact circumstances were that led to the killing, Hela Governor Philip Undialu told the Australian Broadcasting Corporation on Wednesday that the motive behind the killings could be in retaliation for an earlier incident in another village.
Highland clans have fought each other in Papua New Guinea for centuries, but an influx of automatic weapons has made clashes more deadly and escalated the cycle of violence.
The victims in Hela province included two pregnant women and eight children.
William Bando, provincial administrator, requires at least another 100 members of the security forces in support of the current 40 officers.
Police spokesman Dominic Kakas said police were unable to confirm the massacre as they were waiting on information from the local commander.More news: Mojave Desert rupture left by 7.1-magnitude quake is visible from space
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"It modified into retaliation of a outdated attack".
Native data company EMTV reported on the very least two incidents in small villages in the Tari-Pori district.
Local health worker Pills Kolo said it was hard to recognise some of the body parts and posted images of remains bundled together using mosquito nets as makeshift body bags.
The Post-Courier, based in the South Pacific island nation's capital Port Moresby, reported as many as 24 people killed in the villages of Karida and Peta since Saturday.
"In memory of the innocents who continue to die at the hands of gun toting criminals, your time is up".
Grisly photos depicting the aftermath of an ambush killing in the village of Karida in the highland province were shared on Facebook.
"How can a province of 400,000 of us feature with policing regulations and expose with below 60 policemen, and espresso operational protection power and police that does no higher than band abet maintenance", he added.