Chadian and foreign officials in Ndjamena reported fighting around the presidential palace, The New York Times said. But the country's ambassador to the United States, Adam Bechir, claimed President Idriss Deby remained in control and said only a token rebel force had managed to get to the city.
The coalition fighters had been fighting a few miles outside the capital in recent days.
A spokesman posted a statement on the rebels' Web site offering a peaceful resolution. The coalition is "ready to facilitate, with the guarantee of the African Union, the negotiated departure of President Idriss Deby and avoid a pointless blood bath," he said.
Reed Brody, a Human Rights Watch lawyer, said the rebels, who had been living in Sudan, apparently intended their march on the capital in advance of the deployment of a European Union force to provide security for refugees. He said many rebels have ties to past regimes in Chad.
"Nobody is going to miss Deby, but these guys aren't exactly fighting for freedom and democracy," Brody told the Times.