The incumbent Laurent Gbagbo took the oath to serve a new term, but within hours Alassane Ouattara also laid claim to the presidency.

The US, UN and France say last Sunday's run-off poll was won by Mr Ouattara.

He was declared the winner by the electoral body, but this was overturned by the Constitutional Council, which is led by an ally of Mr Gbagbo.

The presidential run-off was intended to reunify the world's largest cocoa producer after a civil war in 2002, but has now left the nation with two rival presidents.

At least four people have been killed in election-related clashes this week in the country's main city of Abidjan.

On the streets opposition supporters are protesting against Mr Gbagbo's investiture, saying it amounts to a coup d'etat.

Mr Gbagbo's supporters insist the UN does not have the right to say who won the elections and have threatened to expel the head of the 8,000-strong UN mission.

Ivory Coast has closed its borders and stopped broadcasts of international news media into the country. An overnight curfew remains in place over the weekend.