Tens of thousands of people are taking shelter in Liberia after fleeing fighting in Ivory Coast, according to the UN Refugee Agency.
Some 300,000 are said to have been displaced within Ivory Coast itself.
Forces loyal to disputed incumbent leader Laurent Gbagbo have admitted that rebels backing his rival Alassane Ouattara have captured the western town of Toulepleu.
They had already taken control of two other towns close to Liberia. People in villages across the border have reported hearing gunfire and say wounded soldiers have been crossing over, seeking treatment.
Gbagbo’s forces say they are regrouping to prepare a counter-attack.
The clashes amid the rebels’ push from north to south are the fiercest since the civil war of eight years ago.
Each side claims its officials’ homes have been ransacked by the other’s supporters.
Hundreds have been killed since November’s election. Gbagbo refused to step down even though Ouattara is internationally recognised to have won.
The UN fears the world’s top cocoa grower is again on the brink of civil war.
Refugees flee Ivory Coast into Liberia