The bodies of 28 people who were shot dead have been discovered in Burkina Faso’s north-western town of Nouna, the government has said.
A civil society group blamed the killings on armed civilians claiming to be members of a government-backed volunteer force fighting jihadists.
The government did not comment on the claim, but said it was investigating.
Burkina Faso has been hit by a decade-long insurgency that has displaced nearly two million people.
The military seized power in Burkina Faso last January, promising an end to attacks, but the violence still rages.
The government said the bodies were discovered on 30 and 31 December.
It condemned the “unacceptable violence” and called for calm, pending the outcome of an investigation.
The incident had occurred at a time when the government had initiated the “mobilisation of the whole people for unity of action in the fight against terrorism”, it added.
The government has formed the Homeland Defence Volunteers (VDP), recruiting civilians into its ranks to fight militant Islamists.
A civil society group, the Collective Against Impunity and Stigmatisation of Communities (CISC), said that armed civilians, claiming to be members of the VDP, carried out the killings in retaliation for an attack by suspected militants between 29 and 30 December.
There is no independent confirmation of its claim.