The Central African Republic's recently toppled president Francois Bozize on Tuesday accused neighbouring Chad of helping the Seleka rebel coalition that ousted him.
"On Saturday March 23 we had destroyed Seleka forces but overnight into Sunday 24, we knew that there had been support from an African country, which I inevitably believe was Chad," Bozize said in an interview with BBC Africa.
"It was Chadian special forces that led the operation on the Sunday morning and attacked the base of the South Africans," he added, referring to troops stationed in Bangui, 13 of whom died in clashes with rebels.
Bozize said his country had "solid brotherly relations" with Chad and was "surprised at their behaviour".
"Only Chadian authorities can give us an explanation," he said.
Chad proved a powerful ally to Bozize during his decade in power, helping him mount a coup in 2003 and fight against rebellions in the north of chronically unstable Central African Republic seven years later.
A recent report from the International Crisis Group also cast doubt on the nature of Chad's relationship with the rebels.
"Chad's position in the conflict is at the very least ambiguous and the Chadian administration is suspected of having dubious relations with the Seleka," it said.
Bozize said he had requested, and been refused, a seat at a summit of the Economic Community Of Central African States (ECCAS), which is holding an emergency meeting to discuss the situation in the Central African Republic in the Chadian capital N'Djamena on Wednesday.
The Central African Republic's new strongman, Seleka leader Michel Djotodia, and his Prime Minister Nicolas Tiangaye will be at the summit.
Bozize fled after a rapid assault on Bangui by Seleka, a loose coalition of three rebel groups, which accused him of failing to implement the terms of a January peace deal.
He has asked for asylum in the west African nation of Benin, according to Beninese Foreign Affairs Minister Arifari Bako.