Forces loyal to Ivory Coast presidential challenger Alassane Ouattara have captured the administrative capital, Yamoussoukro, according to local residents.
Fighting erupted when they later entered the key port of San Pedro on their advance from the north against incumbent leader Laurent Gbagbo, who is clinging to power in the main city, Abidjan, despite losing the presidential election in November.
The United Nations, which recognises Mr Ouattara as the legitimate winner of the election, has voted to impose sanctions on Mr Gbagbo's circle. The EU and African groups have already implemented economic measures against the Gbagbo government.
The UN resolution, drafted by France and Nigeria, imposes a travel ban and assets freeze on Mr Gbagbo, his wife Simone and three close associates.
A million people have fled the violence - mostly from Abidjan - and at least 462 people have been killed since December, according to the UN.
Yamoussoukro's capture is a major symbolic victory for the pro-Ouattara forces, the BBC's correspondent reports, even though it's the capital in name only - all state institutions are still in Abidjan.
The way is now open to Abidjan, less than three hours away along the country's only major highway.