Ivory Coast: Anti-Gbagbo forces close in on Abidjan (UPDATES) (VIDEO)

The U.N. Security Council voted unanimously Wednesday to impose sanctions on Ivory Coast's defiant leader Laurent Gbagbo, as forces loyal to the opposition leader Alassane Ouattara gained control over the capital.

The capture of Yamoussoukro was largely a symbolic victory as Ivory Coast's commercial and political capital is Abidjan, which remains largely controlled by Gbagbo.

Anti-Gbagbo fighters had reached the outskirts of Abidjan on Thursday and were besieging the city, news agencies reported.

The Associated Press reported that Ouattara supporters within the city attacked a prison and freed its inmates, and that the city was divided between Ouattara and Gbagbo’s loyalists.

The army chief of staff, Gen. Phillippe Mangou, sought refuge for himself, his wife and five children in the home of the South African ambassador in Abidjan on Thursday, reported the New York Times, quoting a statement by the South African Department of International Relations. 

Ivory Coast's incumbent president, Laurent Gbagbo, has refused to step down since an election in November in which the international community recognized Alassane Ouattara as the winner.

Gbagbo's forces have been accused of launching attacks and committing a range of rights violations against civilians since the election.

The U.S. on Thursday said Gbagbo would be held accountable for whatever happens in Abidjan.

"If there is major violence in Abidjan and Gbagbo does not step aside, he and those around him, including his wife Simone Gbagbo, will have to be held accountable for the actions they failed to take to stop it," said Johnnie Carson, assistant secretary of state for African affairs, according to Agence France-Presse. "The international community will certainly hold him accountable, but he does have an opportunity, but this opportunity is slipping away."

The U.N. resolution imposes a travel ban and assets freeze on Gbagbo, his wife and closest associates, reports AFP.

"Gbagbo must go, it is the only way to avoid a full-fledged civil war and maybe bloody violence in the streets of Abidjan," France's ambassador Gerard Araud told reporters. France and Nigeria proposed Resolution 1975.

The European Union and African groups have also taken economic measures against Gbagbo to try to force him from power.

The U.N. move comes as forces loyal to Ouattara claimed control over the divided nation's administrative capital, Yamoussoukro.

Citizens greeted opposition troops parading the streets Wednesday with celebratory gunfire.

"People are in the streets waiting for them, clapping for them. There are no soldiers for Laurent Gbagbo in the town now," a resident told BBC.

Opposition forces later entered the key port of San Pedro, it states. Capturing San Pedro would be strategically important because it would enable Ouattara's forces to export cocoa and lumber and have access to the sea to resupply.

More than one million people have already fled their homes due to ongoing violence since the November election, the U.N. estimates.

Read: Ivory Coast refugees flee to Liberia

— Hanna Ingber Win, Freya Petersen