At least 800 people have been killed in the western Ivory Coast city of Duekoue this week according the International Committee of the Red Cross.
Dorothea Krimitsas, a ICRC spokeswoman, told the BBC that they died in inter-communal violence in one district of the western city on Tuesday.
She added that the scale and brutality of the killings were particularly shocking, and appealed to the warring parties in Ivory Coast to remember their obligation to protect civilians.
Fighting has continued in Ivory Coast's main city of Abidjan between the forces of UN-recognised president Alassane Ouattara and those loyal to his rival, incumbent Laurent Gbagbo.
Mr Ouattara's forces have made sweeping gains in the past week but have failed so far to defeat Mr Gbagbo in Abidjan.
Residents say they fear for their safety amid clashes at the presidential palace, TV station and other districts.
France has announced it is increasing its force in Abidjan from about 900 to some 1100.
Troops loyal to Alassane Ouattara, the man internationally recognised as the winner of an election last November, entered Abidjan on Friday.
Mr Gbagbo's whereabouts have been unknown since last week but aides and diplomats suggested he was still in Abidjan.
Mr Ouattara's supporters launched a fresh offensive on Monday, moving from their base in the north. On Wednesday, they captured the capital, Yamoussoukro, and the key port of San Pedro.
UN and French peacekeepers have taken control of Abidjan's international airport.
Many senior military officers, including army General Phillippe Mangou, as well as thousands of soldiers and police, have abandoned Mr Gbagbo.
However, he retains the support of the Republican Guard, special forces and armed militias known as the "Young Patriots".
On Friday, the African Union renewed its call on Mr Gbagbo to stand down.
Last year's election was intended to reunify the country after a civil war in 2002.