Paul Mondouho, the Ivory Coast town of Duekoue's vice-mayor, said authorities had been alerted to the mass grave by a survivor of the attack who recently returned.

On the morning of July 20, a mob descended on the U.N.-guarded Nahibly camp, which housed 4,500 people displaced by the country's recent post-election violence, burning most of it to the ground. Officials said at the time that six people were killed.

"I think there is a link between the July event at Nahibly camp and these new bodies," Mondouho said Thursday. "I think that those people were killed during this event. ... In July some people who escaped the violence gave us the information that many bodies could be found in different wells," he said. "But because of the insecurity in the area, we couldn't investigate that. And the witnesses also fled the place. It's one of them who came back to Duekoue and showed the well in which the six bodies were put."

He added that local officials suspected more bodies might have been hidden in other wells.

The attack was prompted by the shooting deaths of four men and one woman on the night of July 19, according to local officials and residents. The mob of some 300 locals overran the camp on the morning of July 20 after the perpetrators of the shootings reportedly fled there.

The victims in the July 19 attack were members of an ethnic group that largely supported current President Alassane Ouattara in the November 2010 election. By contrast, the camp primarily housed members of an ethnic group that had largely supported Gbagbo. Gbagbo's refusal to cede office despite losing the election to Ouattara sparked six months of violence that claimed at least 3,000 lives.

In the aftermath of the attack on the camp, several witnesses testified to the involvement of members of the Republican Forces of Ivory Coast, the national army created by Ouattara, as well as traditional hunters known as dozos. Both military and dozo leaders denied the claims, saying they had tried to protect the camp.

A Justice Ministry statement read on state television Thursday night said an investigation had been launched to identify the bodies discovered in the well and determine when they were killed.

U.N. spokeswoman Sylvie van den Wildenberg said the U.N. had received a report from civilians on Wednesday that a mass grave may have been found in Duekoue. A joint team of U.N. and Ivorian authorities began investigating Wednesday night and were able to find what appeared to be a human bone, she said.

Ivorian authorities then continued the investigation Thursday, van den Wildenberg said.