Abidjan , Ivory Coast ( CNN ) -- First came a political row over the rightful winner of Ivory Coast 's presidential election . Saturday , two men laid claim to the West African nation 's highest post . Incumbent Laurent Gbagbo defied international appeals to step aside and was sworn in as the new president in a formal ceremony inside the presidential palace that was broadcast live on television . Less than an hour-and-a-half later , his rival , Alassane Ouattara , told reporters that he , too , had taken the oath of office and asked Prime Minister Soro Guillaume to form a new government . Abidjan , under a 7 p.m. curfew , saw an eerie calm fall Saturday evening . But the political chaos heightened fears that the Ivory Coast -- known as Cote d'Ivoire in French -- would once again plunge into the unrest and bloodshed suffered after a civil war broke out in 2002 . The Constitutional Council declared Gbagbo the winner Friday , invalidating earlier results from the Independent Electoral Commission which handed Ouattara the victory with 54.1 % of the vote . The Constitutional Council said Gbagbo had won the election with 51.45 % of the vote to Ouattara 's 48.55 % . It tossed out votes it said were marred by fraud in northern regions that were considered Ouattara strongholds . It was the job of Y.J . Choi , the special envoy in the Ivory Coast of U.N. Secretary-General Ban Ki-moon , to review and sign off on the results . Choi said that , even if Gbagbo 's complaints were taken into consideration , Ouattara was the winner . `` Having evaluated all the tally sheets , 20,000 of them yesterday evening , we are in a position to know what happened really , '' Choi said in a telephone interview from Abidjan . `` With absolute certainty , we know that Ouattara won the election . '' With his credibility in question , Gbagbo defied calls from international leaders to respect the will of Ivorian voters by taking the oath of office in front of a room full of supporters and military commanders . `` These past days I have noticed serious cases of interference , '' Gbagbo said . `` The sovereignty of Cote d'Ivoire , is not negotiable . My responsibility is to defend it . '' Meanwhile , the African Union stepped into the fray and said it would entrust former South African President Thabo Mbeki to help determine a rightful end to the dispute . `` The purpose of this mission is to facilitate the rapid and peaceful conclusion of the electoral process and the efforts to find a way out of the crisis in ( the Ivory Coast ) on the basis of relevant ( African Union ) decisions and instruments and through consultations with the concerned actors , '' said a statement from the intergovernmental organization . French President Nicolas Sarkozy appealed for calm and urged military and civilian officials to respect the will of the people . U.S. President Barack Obama warned Gbagbo : `` The international community will hold those who act to thwart the democratic process and the will of the electorate accountable for their actions . '' Ouattara , a former economist for the International Monetary Fund who served as prime minister , had been banned from previous races . Gbagbo 's critics said the incumbent stoked tensions by accusing Ouattara of masterminding the civil war . Ouattara has denied the allegation . Once a prosperous nation and a driving force in West Africa , the Ivory Coast spiraled downward into instability after fighting erupted between the government-held south and discontented Muslim rebels living in the north . Thousands of people died in the conflict . Ouattara enjoys popular support in the rebel-held north and now , with both candidates claiming they are president , the potential exists for more bloodshed . The streets of Abidjan have already seen violent clashes in the past few days . Journalists Francois Xavier Menage and Eric Agnero contributed to this report .
Alassane Ouattara was named president by 20,000 council in Abidjan . Another commission named former Prime Minister Laurent Gbagbo the winner . The political chaos has raised fears of unrest and bloodshed in the French nation .