At least 800 people are reported to have been killed in the Ivory Coast city of Duekoue this week, as rival forces continue to battle for power.
International Committee of the Red Cross (ICRC) staff visited Duekoue and said the scale and brutality of the killings were shocking.
The city was captured by fighters supporting UN-recognised president Alassane Ouattara this week.
His forces have encircled rival Laurent Gbagbo in the main city, Abidjan.
Mr Ouattara was internationally recognised as president after winning a run-off vote in November, but Mr Gbagbo also claimed victory and refused to leave office.
A curfew called by Mr Ouattara from 2100 GMT to 0600 GMT in Abidjan remains in place. Land and sea borders remain closed, although on Friday the country's air space was reopened.