Rebel forces trying to unseat the Ivory Coast president, Laurent Gbagbo, claim to have captured the town of Toulepleu in the west of the country.
Government sources say fighting is still going on there.
Hundreds have died in Ivory Coast since an election in November. Alassane Ouattara is recognised internationally to have won but the incumbent Gbagbo refused to stand down.
This latest fighting is the heaviest since rebels tried to topple Gbagbo in a civil war eight years ago. Tens of thousands of refugees have fled into neighbouring Liberia.
At the weekend, the UN promised 2,000 reinforcements for the peace-keeping force in Ivory Coast. Two combat helicopters have already arrived. The peacekeepers fired into the air while trying to clear roadblocks set up by Gbagbo supporters who want the UN blue helmets to leave the country.