The United Nations Security Council is holding emergency talks on the situation in Chad, where heavy fighting is raging between rebel forces and government soldiers.
UN officials in New York say Secretary-General Ban Ki-moon is "profoundly alarmed" by the deteriorating situation in Chad's capital, N'Djamena.
With fighting spreading to other parts of the country, Mr. Ban says he also is concerned that life-saving assistance may be interrupted for more than 450 thousand people living in refugee camps in Chad.
Reports from N'Djamena say rebels now hold portions of the city, but that they have not been able to take the fortified palace where President Idriss Deby is holed up. Government helicopters have been carrying out air strikes against the rebels, who have machine guns and cannon mounted on the pickup trucks that carried them into the capital Saturday.
Fighting also is reported in the eastern city of Adre, near the border with Sudan. Government forces say they repelled a rebel assault on Sunday.
Authorities in Chad say that Sudanese helicopters supported the rebel attack on Adre, but Sudan denies its forces were involved. At the same time, Chadian rebels say fighters from Darfur who oppose Sudan's government are trying to help Mr. Deby's forces.
N'Djamena residents say the main market in Chad's capital has been heavily damaged, and that dozens of bodies are lying in the streets. Looters are said to have wrecked the national radio station, which has been off the air since Saturday.
The United Nations withdrew all its staff from Chad - about 150 people - on Friday, including aid workers who help run camps for refugees from Darfur.
France has been organizing airlifts for hundreds of foreign nations from Chad to Gabon's capital, Libreville. French forces control the N'Djamena airport, but rebel fighters are threatening to attack, because they say Chad government helicopters are using the airfield.
EU officials say the fighting will delay deployment of a peacekeeping mission in eastern Chad, aimed at protecting refugees from Sudan's Darfur region.