The massacre, which is being blamed on the country’s security forces, took place last week in the northern village of Karma and surrounding areas.

“We were on the way to the well with my donkey when we saw them moving towards us,” Belem Lassane, a child survivor, told Al Jazeera on Saturday. “We hid in our homes. Our father came out. They took our identifications and started firing at them, killing them all.

“They then destroyed the homes and killed our mothers. I was hiding underneath piles of bodies as they continued to fire at us.”

A prosecutor has launched an investigation into the “massacre”, which took place in the northern village of Karma and the surrounding area after reports that people wearing the uniforms of the Burkinabe armed forces had killed about 60 civilians.

“Our teams have documented and registered 136 dead bodies in Karma, including 50 women and 21 children – some babies under 30 days old killed on their mothers’ backs,” the Collective against Impunity and Stigmatisation of Communities (CISC) said.

The NGO said in a statement that the assailants also killed 11 people nearby the same day – six in Dinguiri village, two in Mene, and three on the road between Ouahigouya and Barga.

The organisation said the attackers in Karma grouped civilians together by the dozens, “taking care to leave armed men with each group with the watchword ‘Kill everyone,’” CISC head Daouda Diallo said.

The attack, one of the worst on civilians as the country battles rebels linked to al-Qaeda and ISIL (ISIS), has provoked condemnation and calls for an investigation by the United Nations Human Rights Office.

Burkina Faso is one of several West African nations struggling with a rebellion that has spread from neighbouring Mali over the past decade, killing thousands of people and displacing more than 2 million.

The military government has launched a large-scale offensive, which it said is aimed at reclaiming swathes of territory controlled by armed groups.

‘Joy shattered’

The government condemned the attack on Karma in a statement on Thursday but gave no details on casualties. Since then, more information has emerged.

Journalist Issa Nappon told Al Jazeera that while many people blame security forces for the killings, it is important to be cautious when assigning blame.

“Many people say it’s the military that attacked them and killed the people. What I’m saying is you have to be very careful … because you have gunmen and armed groups who have military outfits,” he said from Bobo Dioulasso.

A statement issued by residents and survivors on Saturday said the village was surrounded early in the morning of April 20 by heavily armed men in Burkinabe military uniforms who were on motorcycles, pick-up trucks and armoured vehicles.

“The villagers initially rejoiced at their arrival, but their joy was quickly shattered by gunfire,” the statement said, adding that they have counted 136 civilians killed and nine injured.

A representative of the residents and survivors, speaking at a news conference in Ouahigouya, the provincial capital, about 15km (9 miles) from Karma, said the government’s statement bordered on indifference and contempt for residents of the village.

The statement sows confusion about the responsibility of security and defence forces for the massacre, he said.

“We, population and survivors of the events of Karma and surroundings, have no doubt that it is the security and defence forces that are responsible for this carnage,” the statement said. “We are not fooled. We know our security and defence forces well.”