Hundreds of rebels penetrated the capital of Chad on Saturday. The violence has endangered a $300 million global aid operation supporting millions of people in Chad, a country about three times the size of California.
It also has delayed the deployment of a European Union peacekeeping mission to both Chad and neighboring Central African Republic.
France accused Sudan of wanting to crush President Idriss Deby's regime ahead of the arrival of the EU force, which is to operate along the volatile border with Darfur.
The force was to be based in the area of the key eastern town of Adre, which rebels said they seized on Sunday. The government said it had repelled the attack. Adre, near the border with Darfur, is a humanitarian hub surrounded by camps with some 420,000 refugees from Darfur and Chadians displaced in the spillover from the violence.
Chadian Gen. Mahamat Ali Abdallah Nassour alleged that Sudanese troops were involved and called it a "declaration of war" from Sudan.
"Sudan does not want this force because it would open a window on the genocide in Darfur," Chad's Foreign Minister Amad Allam-Mi said on Radio France Internationale.
In a statement Sunday, Sudan's Foreign Ministry spokesman Ali al-Sadeq said "we would like to stress that Sudan does not provide any assistance to any side" in Chad.
"Any developments in Chad reflect on Sudan and any instability there would have a negative impact on Sudan," he said.
The U.S. Embassy in N'Djamena said Sunday it was temporarily closing and relocating all of its operations and remaining staff to the airport. It had authorized the departure of its nonessential staff. The United Nations also said it was temporarily evacuating its staff.
French soldiers in N'Djamena began evacuating foreigners on Saturday night, and nearly 400 had left by midday Sunday, said a French military spokesman, Capt. Christophe Prazuck.
One foreign aid worker described the scene in N'Djamena on Sunday as "bloody and chaotic" with bodies littering the streets and looters breaking into shops during lulls in the fighting. Gunfire could be heard coming from the area around the presidential palace, said the aid worker, who spoke on the condition of anonymity because he was not authorized to talk with reporters.
The death toll from the fighting was not known. But the French organization Medecins sans Frontieres reported they had operated on about 50 wounded people - only one a combatant - since Saturday at a hospital in the capital. A spokesman in Paris said the Chadian Red Cross had told MSF doctors that they had counted about 200 wounded. The civilians had been hit by stray bullets, MSF said.
Hundreds of people are fleeing the fighting, crossing the Chari River to Kousseri, in neighboring Cameroon. Helene Caux with the U.N. refugee agency said at least 400 had crossed and "people are still coming." She said her agency needed to confirm the refugees were civilians with no fighters among them.
The rebels arrived Friday on the capital's outskirts in about 250 pickup trucks mounted with machine guns after a three-day push across the desert from Chad's eastern border with Sudan. The entered the city early Saturday, quickly spreading through the streets.
The fighting resumed around dawn Sunday, a French military spokesman said, and government forces were using tanks and helicopter gunships to try to repel the rebels, who were battling back with assault weapons, rocket-propelled grenades and machine guns.
Several international workers in the Darfur town of el-Geneina in Sudan confirmed that Chadian rebels had left their nearby bases in recent days and were reported to have crossed into Chad. They spoke on condition of anonymity because of the sensitivity of the issue.
French and U.S. statements condemning the coup attempt have referred to the rebels coming from outside the country.
Rebel spokesman Abderaman Koulamallah claimed Deby was trapped at his presidential palace, surrounded by tanks and armored vehicles, and that they controlled the rest of the city after two days of fierce fighting.
"Nobody can say who will win," said Prazuck, the French military spokesman.
France offered to whisk Deby out of Chad, Defense Minister Herve Morin said Sunday. Deby apparently refused to flee.
Chad has been convulsed by civil wars and invasions since independence from France in 1960. The recent discovery of oil has only increased the intensity of the power struggles in the largely desert country, and another Chadian rebel group launched a failed assault on N'Djamena in 2006.
The rebels currently fighting in the city are a coalition of three groups. The biggest is led by Mahamat Nouri, a former diplomat who defected 16 months ago. They others are led Timan Erdimi, a nephew of Deby who was his chief of staff and the third is a breakaway from Nouri's group headed by Adelwahid Aboud. They have long been fighting to overthrow Deby, whom they accuse of corruption.
The rebels are also angry with the president for not providing what they consider enough support to insurgents in Sudan's Darfur region, some of whom are from Deby's own tribe, the Zaghawa, who are found in both Chad and Sudan.
Deby, who came to power at the head of a rebellion in 1990, has won elections since, but none deemed free or fair. He brought a semblance of peace after three decades of civil war and an invasion by Libya, but became increasingly isolated.
The most recent rebellions in Chad began in 2005 in the east, erupting at the same time as Darfur conflict in Sudan. More than 200,000 people have died in five years of fighting between ethnic African tribes and Sudanese government forces and 2.5 million have been driven from their homes.