Chadian soldiers in the Central African Republic killed at least 30 civilians in an unprovoked attack on a market in Bangui last weekend, a UN inquiry says.
Another 300 people in the capital were injured in the shooting, it said.
The troops, who were reportedly on a mission to evacuate some of the city’s remaining Muslim inhabitants, said they were attacked first by militias.
Chad has said it will pull its peacekeepers out of CAR in protest at claims that they aided Muslim rebels.
In the year since the Muslim Seleka rebels ousted the CAR government last March, the country has been engulfed by a wave of religious violence.
Under regional pressure, their leader stepped down in January but attacks have not stopped.
Thousands of Muslims, a minority in CAR, have been fleeing to neighbouring Chad and Cameroon after being targeted by Christian militias, known as anti-balakas.
Chad has contributed roughly 850 soldiers to a contingent of 6,000 African Union peacekeepers tasked with ending the bloodshed.
Rupert Colville, spokesman for the UN’s human rights office, said initial investigations appeared to show that the troops involved in the incident on Saturday were not part of the AU mission.
Chad, which neighbours CAR to the north and has a predominantly Muslim population, also has soldiers in the country helping with the evacuation of Chadian citizens caught up in the chaos.
The troops arrived on Saturday afternoon in pick-up trucks in the northern PK-12 suburb, one of two areas in Bangui where there are still some Muslim inhabitants threatened by the anti-balakas, Mr Colville said.
“As soon as the convoy reached the market area… it reportedly opened fire on the population without any provocation,” he said in a statement.
“At the time, the market was full of people, including many girls and women buying and selling produce. As panic-stricken people fled in all directions, the soldiers allegedly continued firing indiscriminately.”
Mr Colville told the BBC Chadian soldiers had saved many lives during previous evacuations but in this case “for some reason they seem to have just fired on the general population”.
“It’s appalling to shoot in a crowded market place,” he said.
A statement from Chad’s foreign ministry on Thursday said its forces had been the victims of “a gratuitous and malicious campaign” to blame them for “all the suffering in CAR”.
Chad has said its peacekeeping forces will remain in CAR while the details of the withdrawal were worked out.
The ousted president of CAR, Francois Bozize, told the BBC last year that Chadian troops had helped drive him from office, which Chad has denied.
The African Union contingent in the country is backed by some 2,000 French troops.