Rebel fighters on Sunday captured the Central African town of Bangassou, around 750 kilometres from the capital Bangui, the town's head of operations for the UN mission told AFP.
"The rebels control the town," Rosevel Pierre Louis, MINUSCA's regional chief in Bangassou told AFP. "They are everywhere."
The offensive came weeks after rebels were accused of an attempted coup and days before expected results from a tense presidential election.