At least 10 people were killed and dozens wounded when Chadian troops opened fire on civilians in Central African Republic's capital Bangui, officials said on Sunday.
The troops were driving into the city, scarred by religious conflict over the past year, to escort a convoy of Muslims back to Chad, having earlier crossed the countries' border some 500 km (300 miles) to the north in about 15 army vehicles.
"When they got to the PK12 neighbourhood, they suddenly started shooting. People panicked and started running and ducking for cover," said Sebastien Wenezoui, a spokesman for the country's Christian militia, the anti-balaka.
Saturday's shooting was the latest in a string of violent incidents involving Chadian troops, who the anti-balaka accuse of siding with Muslims and Seleka rebels and preying upon the local Christian population.
The mainly Muslim Seleka seized power a year ago, perpetrating abuses on the majority Christian population that triggered waves of revenge attacks, leading to thousands of deaths and displacing hundreds of thousands.
Under international pressure, the rebels gave way in January to an interim civilian government.
But the government - backed by 2,000 French and 6,000 African Union peacekeepers - has been unable to halt attacks by the anti-balaka on Muslims, tens of thousands of whom have fled
to neighbouring countries or sought shelter in camps.
Majority-Muslim Chad has evacuated several thousand of its citizens through airlifts and road convoys. Its government was not immediately available to comment on Saturday's shooting.
The president of the local Red Cross, Pastor Antoine Mbao Bogo, said Chadian troops had fired at civilians.
"I was told over 10 people were killed and about 30 others were wounded, but I have not been able to verify the figures." he said.
Antoinette Montaigne, communications minister for Central African Republic's interim government, said the administration was still waiting for a report about the incident, adding that the government condemned the violence.
Tens of thousands of people have been killed in Central Africa Republic, Human Rights Watch says.
The United Nations estimates about 15,000 Muslims are still trapped in Bangui and other areas in the north, northwest and south of the country, protected by international forces.