Rebel forces pulled out of Chad's captital, N'Djamena, after heavy fighting at the weekend, news agencies report.

But the government and the rebels gave different reasons for the withdrawal.

"The whole of N'Djamena is under control and these mercenaries in the pay of Sudan have been scattered," Interior Minister Ahmat Mahamat Bachir told Radio France Internationale, reported the BBC. However, the Associated Press reported rebel spokesman Abderaman Koulamallah as saying "we decided to retreat to give the population a chance to get out."

Thousands of residents of N'Djamena were streaming out of the city, according to a Reuters report, and the bodies of civilians were lying on some streets. Rebels penetrated the city on Saturday, and the government deployed tanks and helicopter gunships to protect the presidential palace.

The charity, Save the Children, said today that the fighting threatened a U.S. $300 million global aid operation supporting millions of people.

It quoted Gareth Owen, its director of emergencies - who is in Chad - as saying: "The whole humanitarian network in Chad is dependent on planes flying in and out of the capital. As the violence disrupts Ndjamena, children and families across the whole country will suffer."

Save the Children and other aid groups are working in the east of Chad with refugees from Darfur and Chadians who have fled their homes.