This has happened in a sharp escalation of violence ahead of the presidential and parliamentary election on December 27.
Government and UN sources also confirmed the fall of Bambari.
The news sent shockwaves in Bangui where the government of President Faustin-Archange Touadera has been trying to build support for the vote.
President Touadera on Monday said the vote would go ahead as planned, urging people to ignore reports of a rebel advance.
Former president Francois Bozize of backing a new rebel movement keen on overthrowing the government.
Bozize's presidential bid was rejected by the country's constitutional court citing UN sanctions.
Bambari's capture will further complicate matters for the Central African Republic's weak government which has already been struggling to govern.
Bambari is located 380km northeast of the capital Bangui.
Vast areas of the country remain in the hands of militias and rebel groups.
Rwanda and Russia have reportedly rushed in several hundred soldiers to stop the rebel advance.
MNA/PR