(CNN) -- Soldiers from Chad entered a market in the Central African Republic capital of Bangui last week, killed about 30 civilians, wounded another 300 and returned to Chad, according to preliminary findings by the United Nations Human Rights Office.
The incident reflected the growing complexity of the situation in the Central African Republic, a former French colony plunged into chaos last year after a coalition of mostly Muslim rebels ousted President Francois Bozize.
They have since been forced out of power, but Christian and Muslim militias continue to battle for control.
Human rights investigators said the March 29 incident began when Chadian national army soldiers entered Bangui in a convoy of several military pick-up trucks.
They entered a crowded market where shoppers included women and children, and opened fire, a U.N. report said Friday.
"As panic-stricken people fled in all directions, the soldiers allegedly continued firing indiscriminately," said Rupert Colville, spokesman for the U.N.'s office of the High Commissioner for Human Rights.
"Several sources told the investigating team that they believed the Chadian force had entered Bangui to extract remaining Chadians and other Muslim inhabitants in order to save them from further attacks by (Christian militias)," Colville said.
The U.N. said the soldiers who were responsible for the Bangui attack were Chadian soldiers but not among those who are part of the African-led International Support Mission peacekeeping mission that's trying to stabilize the Central African Republic.
"It seems they have gone straight back to Chad without being apprehended," Colville said of the attackers.
About 850 Chadian soldiers are part of the 6,000-strong peacekeeping presence, but on Thursday, Chad's foreign ministry issued a statement saying the country planned to withdraw its troops from the force, according to CNN French affiliate BFMTV.
"Despite the sacrifices we have made, Chad and Chadians have been targeted in a gratuitous and malicious campaign that blamed them for all the suffering in (Central African Republic)," said a statement from Chad's foreign ministry.
Anna Maja Rappard