Haiti s prime minister s office said on Monday that the massacre was ordered by a gang leader who suspected his child had been made ill using witchcraft or black magic, Reuters reported.
"A red line has been crossed," the office said in a statement, adding it would "mobilize all forces to track down and annihilate" those responsible, including Wharf Jeremie gang leader Monel "Mikano" Felix, whom it accused of planning the attack.
It said the victims were mostly elderly.
The National Human Rights Defense Network (RNDDH), an NGO in Haiti that monitors state institutions and promotes human rights education, said on Sunday at least 110 people - all aged over 60 - had been killed in Cite Soleil over the weekend.
RNDDH later said the death toll could be higher because witnesses said "mutilated bodies were burned in the streets, including several young individuals who were killed attempting to save residents."
RNDDH said Felix had ordered the violence after his child became sick, and after seeking advice from a voodoo priest who accused elderly people in the area of harming the child through witchcraft. The group said Felix s child had died on Saturday afternoon.
Reuters was not able to independently verify the events outlined by RNDDH. Felix did not immediately comment on the RNDDH s accusations.
Cite Soleil, a densely populated slum by the port of the capital Port-au-Prince, is among the poorest and most violent areas of Haiti.
Tight gang control, including the restriction of mobile phone use, has limited residents ability to share information about the massacre.
The government, wracked by political infighting, has struggled to contain armed gangs growing power in and around the capital. Gangs are accused of indiscriminate killings, gang rapes, ransom kidnappings and fueling critical food shortages.
Gang violence has killed thousands across Haiti this year as armed groups spread into some of the last parts of the capital that were not already under their control.
A U.N.-backed security mission - requested by Haiti in 2022 and approved a year later - has so far just partially deployed and remains deeply under-resourced.
Haitian leaders have called for the mission to be converted into a U.N. peacekeeping force to ensure it is better supplied, but the plan stalled amid opposition from China and Russia in the Security Council.
In October, another massacre shocked the nation.
The Gran Grif gang took responsibility for the killing of at least 115 people in Pont-Sonde, a town in Haiti s breadbasket Artibonite region. They cited retaliation for residents helping a self-defense group hinder their road toll operations.
Volker Turk, the United Nations High Commissioner for Human Rights, told reporters the weekend s death count had hit 184 in Cite Soleil.
"These latest killings bring the death toll just this year in Haiti to a staggering 5,000 people," he said.
