The latest violence, in which between six and nine people died, occurred during fighting in the central market town of Kaga-Bandoro yesterday, security sources said.
The violence broke out when four ex-Seleka militiamen tried to steal a local radio station's generator and launched reprisals after one of their men was killed.
"Ex-Seleka" is the term used for remnants of the supposedly disbanded alliance of mainly-Muslim armed groups which seized power in CAR in late 2013 before being chased from the capital the following year.
"Let nobody divide us, We want peace for the future of our country," said Nzapalainga, who at 49 was the youngest of 17 new cardinals named by the pope on Sunday.
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The peace march was attended by thousands of Christians and Muslims in the predominantly Christian country.
Last week the murder of an army officer in Bangui's predominantly Muslim PK5 neighbourhood provoked a cycle of violence which left another 11 people dead.
The coup sparked revenge attacks involving Muslim forces and Christian vigilante groups known as "anti-balaka" (anti-machete) militias.
Thousands were slaughtered in the spiral of atrocities that displaced about a tenth of the population of 4.8 million.
Fears of a bloodbath led to a military intervention by former colonial power France and the deployment of UN peacekeepers.
French Defence Minister Jean-Yves Le Drian will visit Bangui on October 30 to officially end his country's military Operation Sangaris, which was launched in December 2013 in a bid to quell violence between Christian and Muslim militias.
President Faustin-Archange Touadera on yesterday renewed his call for militia groups to put down their arms.