The United Nations Security Council is holding an emergency meeting to discuss the deteriorating situation in Chad.

UN Secretary-General Ban Ki-moon has called for an end to fighting in the central African country, where rebels have besieged the presidential palace in the capital, N'Djamena.

"He is profoundly alarmed by the dangerous situation in Chad," a spokesman for Mr Ban said.

"He is particularly concerned at the deterioration of the serious humanitarian situation of some 285,000 refugees and 180,000 internally displaced persons."

Several hundred people have been injured in two days of confused street fighting after a rebel assault, the second to hit the Chadian capital in almost two years.

Troops loyal to Chad's President Idriss Deby struck back at rebels besieging his palace in the capital N'Djamena on Sunday and the government said it repulsed an attack by Sudanese forces in the east.

Government helicopters and tanks defended Idriss Deby's fortified presidential complex against rebels in pickup trucks mounted with cannon and machine guns who stormed into the city.

And on Chad's far eastern frontier with Sudan's Darfur region, the army said it had beaten back a ground and air attack against the border town of Adre by a mixed force of Sudanese army troops and allied rebels and militia.

President Deby's Minister of State for Mines and Energy, General Mahamat Ali Abdallah Nassour, called the attack on Adre "a declaration of war" by Sudan.

Sudan's government denied the accusations from its neighbour that it had backed the offensive by an alliance of Chadian insurgent groups, who denounce President Deby as corrupt and dictatorial.

Former colonial ruler France, which has a military contingent in Chad, said its planes had evacuated more than 500 French and other foreigners to Gabon and would be flying out several hundred more.

Aid group Oxfam has evacuated its international staff from the capital, and said the fighting could hamper humanitarian efforts for half a million people displaced in eastern Chad.

Foreign and local residents in N'Djamena said heavy weapons and machine gun fire erupted before dawn near the presidential palace to the west of the sprawling city on the banks of the Chari river.

During the fighting, prisoners escaped from a main jail and widespread looting was reported across the city.

The rebel leaders include high-level officials who have defected, and who accuse President Deby of favouring his family and Zaghawa clan group in power.

They say Mr Deby, who won elections in 1996, 2001 and 2006, has squandered the country's oil resources, which are being developed by a US-led oil consortium.

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