At least 20 people have been killed in a raid on the remote town of Birao in the north-east of the Central African Republic, according to reports.
The attack comes ahead of a referendum on the constitution and as fears mount that the CAR could soon see an influx of refugees from Sudan's Darfur region.
Officials have blamed the attack on opponents of President Francois Bozize who seized power in March 2003.
The north-east of the CAR has seen raids by Sudanese poachers in the past.
The government has sent troops to the area and says calm has been restored.
The CAR votes in a referendum on the constitution on 5 December and in parliamentary and presidential elections in January.
The last constitution was annulled by President Bozize, when he took over in a coup in 2003.
It is unlikely Bozize (right) will let ex-president Patasse (left) stand in elections
A government statement broadcast on state radio said one of the aims of the attack on Birao was "to disturb the process of restoring normal constitutional life".
General Bozize is expected to stand in the presidential elections.
The former ruling party, the Movement for the Liberation of the Central African People (MLPC), has nominated as its candidate former president Ange-Felix Patasse, who is in exile in Togo, after being ousted by General Bozize.
However, it is unlikely General Bozize will allow him to return to the CAR to stand in the poll.