While so far only 16 fatalities have been confirmed by police, a local journalist spoke of "around 20 dead", while one human rights group warned that the number of fatalities could be as high as 70.
Local rights activists said the Gran Grif gang, one of Haiti's most feared criminal organisations, was behind the deadly attacks, which they said had caused 6,000 people to flee.
Gang violence has ravaged the Caribbean country for years and the multinational police force sent to contain it has struggled to enter areas where gangs hold sway.
Residents of the rural area of Jean-Denis, near the town of Petite-Rivière de l'Artibonite, said that a first attack took place in the early hours of Sunday.They told Haitian news site Le Nouvelliste that gang members had "arrived from all directions", setting houses alight and shooting at those fleeing from the flames.
Survivors described finding bodies strewn on the road the next morning.A second deadly attack reportedly occurred on Monday. So far, 16 bodies have been taken to nearby morgues but with gang members still roaming the area, many locals are too afraid to collect the remains of those killed.
The ombudsman's office said at least another 19 people had sustained bullet wounds, adding that the continued presence of gang members was making it difficult to verify the number of victims.
Romain Le Cour Grandmaison, director of the Haiti Observatory at the non-governmental organisation Global Initiative, told the BBC the attack seemed to have been highly co-ordinated with roads reportedly blocked to prevent police from intervening.
As often in such large-scale attacks, it was preceded by warnings and criticism has been mounting over the authorities' failure to act on these advance signals, Le Cour Grandmaison says.
The attack is believed to have been led by a commander known as "Ti Kenken".
Formerly a leading figure in a vigilante group founded to protect locals from gangs, he switched sides and joined Gran Grif, the Haiti expert explains.
Le Cour Grandmaison warns that "Ti Kenken's" alleged role in the attack raises critical concerns.
"Vigilante brigades are often viewed as essential partners for holding territory and supporting the police - but what happens when allegiances shift?" he asks.
For Le Cour Grandmaison, there is not only a risk of escalating violence in which civilians are increasingly trapped or even targeted directly, but also a danger of further fragmentation where leaders like "Ti Kenken" move fluidly between roles such as vigilante, criminal and police ally.
This is not the first time residents of Artibonite - a mainly agricultural region - have been the targets of gang violence.
In October 2024, members of Gran Grif went on a deadly rampage in Pont-Sondé, accusing residents of the small town of siding with a rival gang.
The death toll in that attack rose to over 100 as more and more bodies were retrieved in its aftermath.
Gran Grif, the gang locals say was behind both the 2024 killings and this weekend's attacks in Petite-Rivière de l'Artibonite, was designated as a Foreign Terrorist Organization by the United States in May of last year.
US Secretary of State Marco Rubio said at the time that Gran Grif, along with the Viv Ansanm coalition of gangs, were "the primary source of instability and violence in Haiti".
Rubio added that Viv Ansanm and Gran Grif's ultimate goal was to create "a gang-controlled state where illicit trafficking and other criminal activities operate freely and terrorise Haitian citizens".
The multi-national police force (MSS) deployed in 2024 to help Haiti's security forces confront the criminal groups has often found itself outgunned and outmanned.