At least 49 people are dead and many other wounded after renewed fighting in western Ivory Coast, the army says.
Duekoue has been tense for several months
The fighting took place near Duekoue, in a cocoa-producing region near the Liberian border.
Local officials and witnesses spoke of shootings and stabbings, and said homes had been set on fire.
Last month, at least 25 people died in ethnic clashes in the area. Ivory Coast has been in crisis since rebels launched an insurgency in 2002.
Thousands of peacekeepers have been patrolling a buffer zone between the rebel-held north and the government-controlled south, under an agreement to try to end the civil war.
The BBC's James Copnall in Abidjan says the west of the country is the region which most threatens the peace process.
At least eight Muslim ethnic Dioulas were killed on Wednesday night in apparent revenge for the earlier killing of at least 40 Christian members of the Guere community.
The Dioulas are seen as pro-rebel, while the Gueres mostly back President Laurent Gbagbo.
An Ivorian army spokesman told the BBC that at least 11 of the dead had been burnt alive.
A Duekoue resident said he had seen as many as 100 wounded people at the town's hospital.
Thousands of people have taken refuge in a Catholic mission in the town.
A local priest told our reporter that there was not enough food for those who have fled their homes, and he was afraid of disease spreading due to overcrowding.
Duekoue is situated just to the south of the so-called confidence zone - a UN-patrolled zone between the army and the former rebels known as the New Forces.
The west is also home to several militias who support Mr Gbagbo and describe themselves as self-defence units.
Last week they agreed to disarm but the process has stalled.
More than 10,00 French and UN peacekeepers in Ivory Coast are charged with maintaining a fragile peace.