United Nations investigators on Friday headed to a soccer field in the besieged neighborhood of Yopougon in Ivory Coast's commercial capital after new reports surfaced that it was being used as a mass grave.

Hamadoun Toure, spokesman for the U.N. mission in Ivory Coast, said by telephone that the Red Cross had received reports from residents that the field was filled with as many as 40 bodies.

"We are told that there is a vast field that is used to play soccer. It is now an open-air cemetery," he said.

The soccer field is located in Yopougon, an area of the business capital that had voted in large numbers for strongman Laurent Gbagbo, who refused to accept his loss in last November's presidential election. He was removed militarily in April after unleashing his security forces on the population. Hundreds of people were killed in the months before he was deposed.

His militias are believed to have taken cover in Yopougon, and the neighborhood was the scene of pitched battles until Thursday. The army now backing the country's democratically elected leader Alassane Ouattara were able to secure the area.

Toure said it's not clear if the dead were killed by Gbagbo's forces, or if they are Gbagbo supporters slain in reprisal killings by forces loyal to Ouattara.

Ouattara was prevented from assuming office during the nearly five-month-long standoff with Gbagbo and had lived under 24-hour guard in a resort hotel. He is scheduled to be sworn in at a ceremony in the presidential palace later Friday.

Gbagbo is under house arrest in Korhogo, a town in the interior. His French lawyers traveled to Ivory Coast this week and are due to accompany him to an interview with the police Friday. He is facing possible charges of war crimes and crimes against humanity committed by the army in the postelection period.