Military forces loyal to the internationally recognized Ivorian president, Allasane Ouattara, were laying siege to the presidential palace in Abidjan on Friday, news agencies reported.

The whereabouts of Laurent Gbagbo, the former president who has refused to step down despite losing an election last November, were unknown.

Agence France-Presse news agency reported that a large explosion, followed by a plume of smoke, took place near the palace at about 9.15 AM, local time.

France 24, the television news service financed by the French government, reported that both witnesses in the area and sources in Gbagbo's camp confirmed that there had also been fighting around Gbagbo's residence elsewhere in Abidjan. One witness from the Cocody district of Abidjan told France 24 that "heavy gunfire" had gone on "all night long".

The French ambassador to Cote d'Ivoire, Jean-Marc Simon, told AFP that a boat filled with people had been seen leaving the palace and heading for the Charles de Gaulle bridge on Thursday afternoon, but he could not ascertain who was on the boat.

Gbagbo's European representative, Toussaint Alain, said Gbagbo was on Ivorian soil. Alain said he was in regular contact with Gbagbo but would not say where he was.

Also on Friday, African Union leader Jean Ping called on Gbagbo to step down immediately. Earlier, Alain had said Gbagbo had "no intention of abdicating to rebels".