At least 68 bodies were spread out across 10 burial mounds in a mass grave discovered on a football field in the Ivory Coast capital Abidjan, the UN has said.
Guillaume Ngefa, deputy director of the human rights division of the UN mission in Ivory Coast, said the victims were probably killed by pro-Laurent Gbagbo militias on April 12, the day after the strongman was arrested.
Mr Ngefa said that investigators visited the site on Friday and photographed the 10 plots. They interviewed witnesses who described the killings as well as family members who identified the dead.
Mr Ngefa said the investigators spoke to two residents of the Yopougon neighbourhood where the incident occurred who were conscripted by the militiamen and forced to bury the dead.
The killings occurred after Gbagbo was arrested by the army fighting to install the nation's democratically elected leader, Alassane Ouattara.
Yopougon, where the soccer field is located, is believed to be where Gbagbo's militias took cover after their leader's fall.
The area has historically been a Gbagbo stronghold, but it has pockets inhabited by the Djola and Baole, ethnic groups that voted for Mr Ouattara in November's divisive election. The victims were almost exclusively from these two groups, witnesses said.
Mr Ngefa said the largest grave is believed to hold 31 bodies; another has at least 21.
The killings may have been in revenge for the arrest of several dozen militiamen who had taken cover inside a Baptist Church in Yopougon, said Mr Ngefa.