N'DJAMENA - Central Africa's post-coup crisis will come under the spotlight at a regional summit in Chad on Wednesday, as ousted leader Francois Bozize accuses his former Chadian allies of backing the rebels who unseated him.

South African President Jacob Zuma will attend the extraordinary summit as he faces prickly questions over the presence of his troops in the country, 13 of whom were killed in the bloody battle for Bangui.

Bozize, who fled Bangui in the face of the assault by the rebel Seleka coalition a little over a week ago, has accused Chadian special forces of leading the fighting, in an interview with BBC Africa.

His charges came as the region's military giant hosts a meeting of the Economic Community Of Central African States (ECCAS) to find a way to legitimise the rebel regime.

A diplomatic source said the bloc sought to create a national transition council led by rebel president Michel Djotodia and "regain a little international legitimacy."

The international community is expected to press Djotodia for guarantees that he will leave power in 2016, when he has promised elections, and possibly accelerate the transition.

Ousted leader Bozize said he had been refused a seat at the summit, which will be attended by Djotodia's Prime Minister Nicolas Tiangaye.

Observers have said Bozize appears to have been left in the lurch by Chad, a once-powerful ally which helped him mount a coup in 2003 and fight against rebellions in the north of his chronically unstable nation seven years later.

"It is difficult to believe (Chadian President) Idriss Deby did not know about it. If he didn't encourage it, he let it happen," said a source close to the rebellion, adding Chadian sympathisers had provided financing.

A recent report from the International Crisis Group said Chad's position in the conflict was "at the very least ambiguous and the Chadian administration is suspected of having dubious relations with the Seleka."

Some 400 Chadian soldiers formed part of a multinational African peacekeeping force (Fomac), sent to stabilise the country in 2008 and boosted by other troops in January as the rebels closed in on the capital.

However it was not the Chadian troops, but South African soldiers stationed in the capital who came up against the rebels on March 23-24, leading to the deaths of 13 troops and a scandal in Pretoria.

"It was Chadian special forces that led the operation on the Sunday morning and attacked the base of the South Africans," Bozize told BBC.

Bozize fled after a rapid assault on Bangui late last month by Seleka, a loose coalition of three rebel groups, which accused the president of failing to implement the terms of a January peace deal.

He was last reported in Cameroon, seeking asylum in the west African nation of Benin.

South Africa's heaviest military loss since apartheid has raised prickly questions for Zuma over why his troops were sent to an area where South Africa has no immediate strategic interests.

The ICG has said it is the first time South Africa has ventured militarily beyond the south and Great Lakes region.

South Africa's main opposition has demanded an immediate pull-out of the troops while local media reports suggest the soldiers were protecting private business interests.

Zuma on Tuesday dismissed these as "conspiracy theories", saying a contingent was sent to train local forces and provide protection for the now deposed Central African president Francois Bozize under a 2007 deal.

Central African sources close to the presidency and security sources say Zuma and Bozize had signed accords "giving South African businesses access to oil, diamond and gold riches."

In exchange, South Africa would defend Bozize's regime.

"Bozize's accords with South Africa were not in the interest of the country but in keeping Bozize in power. They lost militarily. They must leave and forget about it," a leading Seleka rebel said.