Former South African President Thabo Mbeki is due to arrive in Ivory Coast on Sunday to help mediate a disputed election result.
Incumbent Laurent Gbagbo was sworn-in as Ivory Coast president on Saturday, despite the electoral commission declaring his rival, Alassane Ouattara, winner of a 28 November poll.
Mr Ouattara submitted a rival oath to undertake the presidency and said he would start a parallel government.
The Constitutional Council, which has the final word on the poll and is headed by an ally of Mr Gbagbo, cancelled hundreds of thousands of votes in Ouattara strongholds, on grounds of intimidation and fraud by rebel soldiers who run them, and declared Laurent Gbagbo the winner.
The election result had been certified by the United Nations which said that even if all the allegations of fraud were true, they still could not have changed the result announced by the election commission.
The resulting dispute appears to have scuppered efforts to re-unify the country.
Small-scale protests and tyre-burning broke out on Saturday in several towns, including the largest city, Abidjan, and in Bouake in the north.
New Forces rebel commander Cherif Ousmane warned that his followers would "not rest for long without doing something" about Laurent Gbagbo if he continues to hold power. He did not specify what that would entail.
The poll was meant to unite Ivory Coast after a 2002-2003 war left its north in rebel hands, but that now appears unlikely.
At least 15 people have been killed in election-related violence.
Mbeki hopes for peaceful resolution
South Africa's ambassador to Ivory Coast Zodwa Lallie said the main aim of Mr Mbeki's visit was to seek a peaceful resolution to the row.
He noted similarities with Kenya's election in 2007, in which a disputed result quickly degenerated into ethnic bloodshed that killed at least 1,300 people and displaced hundreds of thousands.
Mr Gbagbo has controlled the world's top cocoa grower for a decade but now faces international isolation and possibly sanctions, after his win was rejected by the United States, the United Nations, France, the European Union, the African Union and West African bloc ECOWAS.