Chadian rebels have entered Chad's capital N'Djamena and are battling against army units near the presidential palace. This follows a one-week rebel offensive to topple long-term President Idriss Deby. VOA's Nico Colombant reports from our regional bureau in Dakar.

Military officials, rebels and international aid workers confirmed the fighting around the presidential palace.

Clashes began early Saturday 20 kilometers outside the capital, before engulfing the city center. Residents in N'Djamena say they heard increasingly intense heavy arms fire. They say rebels occupied the east and south of the capital, and that there was fighting around the airport as well.

An exiled rebel spokesman who has been in contact with rebels on the ground, Makaila Nguebla, says Chad's army has offered little resistance.

He says rebels from several groups who allied themselves for this offensive were able to cross Chad over the course of one week from their bases near Sudan and enter the capital in one day.

The rebels say that if they take over, they will impose transitional rule for two years before organizing free and fair elections. Chad has had several coups since independence from France in 1960.

The newly-elected head of the African Union, Gabon's Foreign Minister Jean Ping, said he was very worried by the situation. He also said the African Union would not accept an unconstitutional change of government.

President Deby has been in power since 1990. Several years ago, he changed the constitution to allow unlimited presidential terms. He went to the scene of fighting Friday, before returning to the capital. Military officials who spoke to media did not immediately disclose his location.

His rule has been marked by accusations of corruption in the newly-emerging oil sector, and lately by defections from his clan-based inner circle to various rebel movements.

The French army, which has a permanent military base in Chad, has been giving the Chadian army logistical and surveillance support, but has said it will not enter into direct combat with rebels.

The fighting has led to the postponement of the deployment of a planned European Union peacekeeping force to secure people displaced from the conflict in Chad, as well as fighting in nearby Central African Republic, and from Sudan's warring Darfur region.

Border regions at the intersection of these three countries have been wracked by different rebellions, attacks by vigilante groups and inter-ethnic communal fighting in recent years.