Rebel forces supporting the internationally recognised leader of Ivory Coast have seized the strategic cocoa-exporting port of San Pedro, residents said.
They said soldiers firing into the air retreated in trucks as the rebels moved into the town about 186 miles west of Abidjan, Ivory Coast's largest city.
The victory came the same day rebels seized the administrative capital, Yamoussoukro.
San Pedro is Ivory Coast's second-largest port and the major export point for cocoa. Ivory Coast is the world's largest cocoa producer.
Incumbent leader Laurent Gbagbo refuses to accept defeat and hand power to Alassane Ouattara, who was declared the winner of November presidential elections.
The United Nations Security Council has demanded an immediate end to the escalating violence and imposed sanctions on Gbagbo, who has refused to relinquish the presidency, and his inner circle.
Wednesday's security council vote was unanimous and came five days after France and Nigeria introduced a draft resolution expressing "grave concern" that the west African nation could relapse into civil war.
"I think the sense of urgency is obvious since ... the confrontation is extending in Ivory Coast and the situation is worsening by the hour," France's UN ambassador Gerard Araud said. The message "is very simple - Gbagbo must go. It is the only way to avoid a full-fledged civil war".
The UN's most powerful body voted on the day that fighters supporting Mr Ouattara seized control of Yamoussoukro.
The resolution demanded "an immediate end to the violence" and urged all Ivorian parties "to respect the will of the people and the election" of Mr Ouattara as president.
It condemned Gbagbo's decision not to accept the solution proposed by a high-level African Union panel earlier this month, which includes recognising Mr Ouattara as president, and urged him step aside immediately.
The African Union had also suggested getting Mr Ouattara to appoint members of Gbagbo's political party to a unity government. Mr Ouattara said he had embraced this idea since last year's presidential campaign, but Gbagbo rejected it.
The resolution backs the African Union proposal and calls for "an overall political solution that preserves democracy and peace and promotes lasting reconciliation among Ivorians".