The head of the African Union is due to arrive in the Central African Republic for talks as rebel forces continue to advance towards the capital Bangui.The AU says Thomas Boni Yayi will discuss the crisis with President Francois Bozize.Earlier, the Seleka rebel alliance entered the central city of Sibut after the army withdrew on Friday evening.Regional leaders say both sides have agreed to hold talks, although no firm timetable has been given.Observers say Mr Boni Yayi is expected to try to persuade President Bozize to launch a dialogue with the rebels.More troops from the Central African Multinational Force (Fomac) arrived in CAR on Saturday to reinforce a contingent already there.More than 100 French paratroopers have also been sent in. However, France insists they are only there to secure its nationals - not to save the regime.A senior UN official said that all its international staff have been evacuated to neighbouring Cameroon.The US has also evacuated its embassy in Bangui.Observers say there was no fighting when rebels entered Sibut on Saturday.The city is about 150km (95 miles) from Bangui.Government troops and Chadian soldiers deployed as a buffer force had left their position hours before and a rebel spokesman said they took over the city because it was abandoned.The spokesman said the rebels had no intention to march on the capital ahead of talks meant to start early next month.However, there is a growing fear that the rebels may well attempt to depose President Bozize.Government troops are reported to have fallen back to Damara, 75km from Bangui, the last major town on the road to the capital.