The killings took place when the Banunu and Batende communities reportedly clashed in four villages in the Yumbi territory of Mai-Ndombe province between Dec.14 and 16, the UN said, citing “allegations from credible sources.”

At least 82 people were injured during the attacks, according to the reports, but the actual number of casualties was expected to be higher, the UN said in a statement.

Some 465 houses and buildings were burnt down or pillaged, including two primary schools, a health centre, a health post, a market and the office of the electoral commission, the UN said.

Thousands of people were reportedly displaced by the violence, including an estimated 16,000 people, who sought refuge by crossing the Congo river into the neighbouring Republic of Congo.

The UN Human Rights Office said it was investigating the reports, calling them “alarming”.

The reason for the clashes remained unknown on Wednesday, but the killings took place only days before a hotly contested presidential election, initially scheduled for Dec. 23 and later at short notice postponed amid political turmoil to Dec.30.