Central African Republic soldiers clashed with rebels seeking to overthrow President Francois Bozize and a rebel commader said 27 fighters were killed.
It was the heaviest combat between government and rebel forces since Bozize, in power since 2003, won a January 23 election that opposition figures said was rigged.
"The fighting was heavy and we killed 22 of Bozize's soldiers and injured many. On our side, we lost five men and had many wounded," Issene Abdoulaye, a commander for the CPJP rebel group, told Reuters by telephone.
A CAR military official confirmed the fighting, which took place near the northeastern town of Sekikede on Sunday and into Monday, but he declined to comment on casualties.
"For the moment, clean-up operations in the zone continue and we can not give an exact number of dead," he said, asking not to be named.
CPJP rebels are the only of many insurgent groups in the former French colony to have refused to sign a peace deal with Bozize's government.
Last November, CPJP fighters occupied the town of Birao for two days before tanks and helicopters from neighboring Chad crossed the border to dislodge them. A U.N. peacekeeping force charged with securing parts of Chad and CAR -- including Birao -- had ended its mission days earlier.
CAR is rich in unexploited minerals, but has been caught up in the conflicts of neighbouring Chad, Sudan and Democratic Republic of Congo.