French military aircraft hovered over the strategic town of Sibut, 180 kilometres (110 miles) north of the capital Bangui, which was seized by ex-Seleka rebels on Thursday, prompting African troops and hundreds of frightened residents to flee.
"A military operation is happening in Sibut," a French communication officer told AFP, while a defence official in Paris confirmed the presence of the aircraft since Friday afternoon.
Newly installed interim president, Catherine Samba Panza, slammed the rebel efforts, saying they aimed to "destabilise her mandate."
"At the time when the government is calling for togetherness, tolerance and national reconciliation, some of our countrymen are taking upon themselves the heavy responsibility of dividing the country," she said.
No Central African citizen "worthy of the name" would allow such "anti-patriotic, irresponsible and dangerous" actions, she added, vowing not to cede "an inch of our ground."
The installation of a new government in the strife-torn nation has failed to stem inter-religious violence between the mostly Muslim Seleka and Christian militia groups.
Tensions remain high in Bangui, where Red Cross officials said they had collected 30 bodies in the past three days after fighting which also left 60 people wounded.
The head of the International Committee of the Red Cross delegation Georgios Georgantas said he was very concerned by an "unprecedented level of violence".
The poor, landlocked country descended into chaos 10 months ago after Seleka overthrew the government and installed one of their leaders, Michel Djotodia, as the country's first Muslim president.
His Seleka fighters began targeting people from the Christian majority, prompting the emergence of self-defence groups that launched revenge attacks on Muslims amid reports of murder, mutilation, rape and looting by both sides.
By the time Djotodia was effectively ousted by regional leaders on January 10 for his failure to end the spiralling bloodshed, about a million people were displaced in a population of 4.6 million.
Georgantas urged the authorities and some 7,000 French and African troops based near Bangui Airport to "take up their responsibilities" and keep the peace in a city abandoned by hundreds of thousands of residents.
The foreign soldiers were patrolling districts of the capital, where French troops this week warned looters that they would open fire if they failed to disperse.
'Villages deserted, people terrorised'
However the interior of the country is a lawless zone ruled by warlords, with few or no foreign troops present.
Doctors Without Borders said this week some of its emergency teams had reported "that some villages remain deserted and people are terrorised."
Albert, a resident of Sibut, is one of hundreds who fled the town when a convoy of Seleka, "armed to the teeth", first arrived on Wednesday night, attacking civilians before moving in a day later.
"As I speak to you, I am hiding in the bush, about 10 km from Sibut. Ninety-nine percent of the inhabitants are in the bush, there is no one left in town," he told AFP by telephone.
"They have committed destruction, robberies in broad daylight, they break down doors, they loot, they clean out suburbs. Bad luck for you if they find you!" he added.
With military efforts under way to regain control of Sibut late on Friday, French army spokesman Lieutenant-Colonel Thomas Mollard said French forces were "supporting (African peacekeeping force) MISCA, which is the leader of the operation".
African leaders and Western diplomats are set to hold a donors' conference in Addis Ababa on Saturday to raise funds for the African Union-led military mission known as MISCA, which is expected to be 6,000-strong by the end of March.
Samba Panza has called for more international troops.
"What we hope is strong support for MISCA, to enable it to implement its mandate more effectively," the director of the AU peace and security council, El-Ghassim Wane, told AFP in the Ethiopian capital.
The violence has created a massive humanitarian crisis, and the UN World Food Programme said in Geneva it urgently needed $95 million to provide food assistance to the population.
The European Union meanwhile pledged 45 million euros ($61 million) in fresh funding on Friday, just over half of which would be used to back the MISCA mission, EU officials said.
The EU has already committed around 150 million euros to the crisis, and this month approved a 500-strong force to be deployed in CAR.