The bloodbath unfolded on April 20 in the village of Karma, in a part of the country that has been badly hit by jihadists, but it was only officially disclosed on Sunday.
Regional prosecutor Lamine Kabore told AFP "about 60 people" were killed by assailants dressed in army uniforms.
But in a statement issued on Tuesday, survivors and local residents said more than 100 died, in a massacre that lasted hours.
Ravina Shamdasani, spokeswoman for the UN's high commissioner for human rights, meanwhile said in a press release that according to reports "at least 150 civilians" may have been killed.
The survivors said that at around 7:30 am last Thursday, the village of some 400 people was surrounded by a "large number of men in uniform," arriving on motorbikes, pickup trucks, armoured vehicles "and a tank."
Some villagers went out to welcome them, happy to see that "these soldiers" had arrived, but the mood swiftly turned to terror as the killings began, the statement said.
"Several people were shot down where they stood without any form of process... women, children and the elderly," it said.
People who tried to hide were ordered to come out, as assailants smashed down doors and set fire to storage buildings.
"Wounded people who tried to flee were pursued and killed... and some women were executed as they were carrying their babies on their back," the survivors said.
The killing lasted until around 2:00 pm, when the soldiers moved off in a column towards Dinguiri, a village lying to the north of Karma, they said.
The community said the dead were still lying in the open as of Tuesday. They had tried to go to the village to bury the bodies on Monday morning, but the army had blocked off the road.
The massacre occurred a week after 34 defense volunteers and six soldiers were killed by suspected jihadists at Aorema, a village about 40 kilometers from Karma.
Following that attack, Burkina Faso's military junta declared a "general mobilization" to give the state "all necessary means" to combat a string of bloody attacks blamed on jihadists affiliated with Al-Qaeda and the Islamic State group.
Kabore said he was investigating the killings and had given instructions for anyone involved to be detained.
Shamdasani called for a fast and rigorous inquiry.
"This investigation must be prompt, thorough, independent, and impartial and must result in credible prosecutions, if such gross violations are to end," she said.
Karma lies in a gold-rich area that has drawn an influx of illegal miners, close to the border with Mali - the epicenter of an 11-year-old jihadist insurgency that has rocked the fragile Sahel.
The violence has left more than 10,000 people dead, according to non-governmental aid groups, and displaced two million people from their homes.
Anger within the military at the mounting toll sparked two coups in 2022, the most recent of which was in September.
The latest strongman, Captain Ibrahim Traore, has declared a goal of recapturing the 40 percent of the country's territory which is controlled by jihadists.
Burkina Massacre Survivors Describe Horror
OUAGADOUGOU - Survivors of a massacre in northern Burkina Faso have described an hours-long ordeal in which men in army uniforms carried out brutal and arbitrary killings, including women who were carrying their babies on their backs.