NAIROBI, Kenya — Chadian rebels said they had seized an eastern town in an area housing more than 400,000 refugees along the border with Sudan's war-ravaged Darfur region, but the government said Sunday it had repelled the attack.

Rebel spokesman Abderaman Koulamallah said he had no other information because he had been fighting all day in N'Djamena, the capital of the former French colony in Central Africa, where rebels were battling for a second day to oust President Idriss Deby.

"We defeated the garrison there and took Adre at around 4 p.m.," Koulamallah said.

But Chad's Gen. Mahamat Ali Abdallah Nassour said government forces fought off the attack, and claimed that Sudanese troops were involved.

Speaking on Radio France Internationale, Nassour said the troops attacked Adre from the ground and air, fighting alongside insurgents and militias. He called it "a declaration of war" by Sudan.

The governments of Chad and Sudan accuse each other of backing the other's rebel groups.

The U.N. refugee agency has 12 camps in that area for 420,000 refugees from Darfur and Chadians displaced in the spillover from the violence in Sudan.

The rebels arrived on the capital's outskirts Friday after a three-day push across the desert from Chad's eastern border with Sudan. Backed by 250 pickup trucks mounted with machine guns, between 1,000 and 1,500 insurgents entered the city early Saturday, quickly spreading through the streets.

A French military spokesman, Capt. Christophe Prazuck, said the fighting resumed around dawn Sunday, and government forces were using tanks and helicopter gunships to try to push out the rebels, who were battling back with assault weapons, rocket-propelled grenades and machine guns.

A 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 U.S. State Department condemned the rebel's attempt to seize power.

"We call for calm in the capital and support the (African Union's) call for an immediate end to armed attacks and to refrain from violence that might harm innocent civilians," spokesman Sean McCormack said.

The violence has endangered a $300 million global aid operation supporting millions in Chad, and also delayed the deployment of the European Union's peacekeeping mission to both Chad and neighboring Central African Republic.

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 believed to be a coalition of three groups. The biggest is led by Mahamat Nouri, a former diplomat who defected 16 months ago, and a nephew of Deby's, Timan Erdimi. They have long been fighting to overthrow Deby, whom they accuse of corruption. Deby, himself a soldier, has seen many defect from the army, where morale is low.

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.