The damning findings came a day after Chad - under fire over the Saturday attack, which also left 300 people wounded -- angrily announced it was withdrawing from the African peacekeeping force struggling to restore security in the strife-torn state.
An investigation into the attack found the Chadian troops had "opened fire on the population without any provocation," said a spokesman for the UN's human rights arm.
"As panic-stricken people fled in all directions, the soldiers allegedly continued firing discriminately," the spokesman, Rupert Colville, said.
"Why they start shooting like this in the marketplace is not clear," he added.
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The attack apparently ended when Congolese peacekeepers arrived, said Colville.
Chadian soldiers in the 6,000-strong MISCA peacekeeping force have reportedly been jittery. MISCA says local militiamen have staged targeted attacks on the Chadian contingent.
Chad said yesterday it was pulling its troops from MISCA because of "a wanton and malicious campaign" against them.
Chad has always denied the charges, and has said it wants to keep working with the neighbouring country to rebuild security there.
The Central African Republic expressed regret today at the decision by Chad, one of the largest contributors to MISCA with about 850 soldiers on the ground.
But many Christians blame the Chadian troops for stoking strife, and say they will be glad to see them go.