The U.N. peacekeeping mission in Ivory Coast, known by its French initials UNOCI, said fighting between government forces and armed militias left six people dead in the western region of Vavoua.
Bert Koenders, U.N. special envoy to Ivory Coast, said the clashes were regrettable, adding the peacekeeping mission has dispatched a team to investigate the violence.
"UNOCI launches an appeal to the competent authorities to have appropriate investigations carried out to determine the circumstances surrounding the incidents, identify those responsible and take adequate measures in keeping with the law," the mission said in a statement.
Liberian mercenaries fighting in support of former President Laurent Gbagbo were blamed for some atrocities committed in Ivory Coast during the political conflict that gripped the West African country early this year.
At least 13 civilians and one Ivorian soldier were among those killed in November near the Liberian border.
Ivorians voted for members of the legislative assembly in mid-December, about a year after rival claims to the presidency pushed the country to the brink of civil war.
Thousands of people were killed and many more were displaced in the conflict, which ended with Gbagbo's arrest in April.