The fighting near Sibut, a market town some 180 kilometres north of Bangui, erupted after Seleka rebels ignored an ultimatum to halt their advance on Bangui, the source told AFP on condition of anonymity.
French troops also took part in the operation against the Seleka fighters, the French army said.
There were no immediate reports of any casualties.
The unrest began yesterday when "continued automatic weapons fire could be heard" around Sibut, said the military source who did not wish to be named.
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Colonel Gilles Jaron, a spokesman for the French army, said at a press briefing in Paris today that France's Sangaris military force had received a "request for support" from the MINUSCA peacekeepers near Sibut as the rebels were advancing.
"We sent a Tiger helicopter, and returned fire on one of the armed groups. Since then, MINUSCA did not ask for more assistance."
MINUSCA has not confirmed the operation.
The 2013 ouster of Christian president Francois Bozize by mainly Muslim Seleka fighters sparked a conflict that claimed thousands of lives and caused nearly half a million people to flee the chronically unstable country.