The Swiss-based International Committee of the Red Cross has said around 800 people were killed in clashes in a western Ivory Coast town in the last week.
ICRC officials visited the Carrefour area of Duekoue on Thursday and Friday to assess needs and gather testimonies, a statement said on Saturday.
"Our colleagues saw hundreds of bodies. We strongly suspect that was the result of intercommunal violence. Since Monday or so, tens of thousands of people have fled the area," ICRC spokeswoman Dorothea Krimitsas told Reuters news agency.
Dominique Liengme, head of the ICRC delegation in the country, described the incident as “particularly shocking in its scope and brutality".
However the United Nations mission in Ivory Coast put the number of deaths at 330, and said the majority were killed by supporters of the country's internationally recognised president Alassane Ouattara.
The area has been a hotbed for conflict between two tribes that support rival leaders seeking power; Ouattara and incumbent Laurent Gbagbo, who refuses to accept his defeat at elections in November.
According to the ICRC, thousands have been killed or injured in post-election violence since November, which has driven up to a million people from their homes in Abidjan alone.
Fierce fighting spread across Abidjan on Friday as troops loyal to Gbagbo fended off attacks by forces supporting Ouattara's claim to the presidency.
swissinfo.ch and agencies