Paris, however, plans to keep 1,000 troops permanently based in Mali to protect energy-rich North Africa. Meantime, months of fighting lie ahead.
Deby claimed Chad's 2,200-man intervention force, is being drawn down -- a mechanized battalion has reportedly already pulled out -- because the nature of the conflict in Mali has changed.
"Face-to-face fighting with the Islamists is over," Deby said last weekend in an interview with French media. "The Chadian army does not have the skills to fight a shadowy, guerrilla-style war that is taking place in northern Mali."
The withdrawal of the Chadian forces, regarded as probably the best trained desert fighters outside of regional military heavyweight Algeria's Special Forces, seriously weakens the French-led forces but that condition may not last long.
There are some 4,000 African troops from Nigeria, Burkina Faso, Senegal, Ghana, Guinea, Niger and Togo in Mali with the French, who're trimming down their force.
But the Financial Times reported "there are concerns about the capability of these troops to hold ground if most of the French and Chadian soldiers leave."
Michael Sheehan, assistant U.S. secretary of defense for special operations, told a congressional hearing in Washington the African component "is a completely incapable force. That has to change."
Mali's army is weak, badly equipped and poorly led and isn't likely to be committed to fighting the agile and seasoned Islamist fighters of al-Qaida in the Islamic Maghreb without the French to provide momentum in the field.
French President Francois Hollande says that by the end of the year French forces will be reduced to the envisaged 1,000-strong garrison.
There are expectations a U.N. peacekeeping force of up to 10,000 overwhelmingly African troops will be in place by then. A U.N. Security Council resolution mandating a complex new peacekeeping force is likely this month.
But in the meantime the French are very much holding the line on their own with the departure of the Chadians, who Paris views as the only regional force sufficiently trained, equipped and capable of offensive desert operations.
Meantime the French, backed by Niger's French-trained battalion, launched a major operation north of the strategic city of Gao, where the Islamists are reported to have infiltrated, on April 7.
French officials say that, out of the 1,500-2,000 militants estimated in Mali in January, more than 600 have been killed.
But by all accounts, AQIM has no shortage of recruits from North Africa and beyond and Sheehan says its leadership is largely intact. So no early end to the conflict is expected.
Deby offered no further explanation why troops who'd been trained in counter-insurgency warfare by U.S. Special Forces under a regionwide program to bolster African armies' capabilities, couldn't cope with jihadists led by AQIM.
At least 30 Chadian soldiers have been killed since they joined a 4,000-strong interventionist task force the French deployed Jan. 11.
They notched up notable successes as the jihadists were driven from southern Mali, where they were threatening the capital Bamako, hundreds of miles into the northern Adrar des Ifoghas.
Deby claimed in March that his forces had killed AQIM's feared field commander, Mokhtar Belmokhtar, a one-eyed veteran of the 1979-89 Afghanistan war against the invading Soviets. But there has been no conclusive proof that the long-elusive Belmokhtar is dead.
Another AQIM leader, Abdeklhamid Abou Zeid, the most dreaded of the organization's chieftains, was killed in the Adrar des Ifoghas in late February. The French confirmed his death.
Roland Marchal of France's National Center for Scientific Research in Paris, says the Chadian combat losses were probably an element in Deby's decision to pull out.
But he added: "There are not many more victories to claim and Chad does not want to get bogged down."
Neither did the French. When Hollande sent in troops in January to prevent the Islamists taking over all of Mali, he said they'd be there for "weeks."
But now he's had to accept he'll need a more permanent force in Mali to ensure the jihadists don't reassert themselves and establish a haven from which to mount transnational operations, an abiding European and regional fear.