President Francois Hollande said Thursday that French troops would be deployed to the Central African Republic immediately, as deadly clashes killed nearly a 100 people.
France's contingent of 650 troops already in the country would be "doubled within a few days, if not a few hours," Hollande said.
Hollande's announcement came after the UN Security Council authorized French and African troops to use force to protect civilians in CAR.
Rival militia forces clashed in the country's capital, Bangui, on Thursday. A Reuters witness at one hospital said he saw least 23 dead and 64 wounded in shooting since dawn. Another eye witness saw dozens of dead elsewhere.
Agence France-Presse correspondents reported seeing almost 80 bodies lying in a mosque and its surrounding streets in Bangui after overnight violence.
The mosque held 54 bodies that appeared to have knife and gun wounds, laid out in the prayer hall and the courtyard. In nearby streets, journalists counted 25 abandoned corpses.
Later, the Associated Press cited witnesses and aid groups saying at least 98 had died in clashes.
The UN resolution also imposed an arms embargo on the country and asked the United Nations to prepare for a possible peacekeeping mission.
In a unanimously adopted resolution the 15-member council also asked UN Secretary-General Ban Ki-moon to establish an inquiry into human rights abuses in the landlocked, mineral-rich nation of 4.6 million people, which slipped into chaos after Seleka rebels ousted President Francois Bozize in March.
The UN resolution expressed "particular concern at the new dynamic of violence and retaliation and the risk of it degenerating into a country-wide religious and ethnic divide, with the potential to spiral into an uncontrollable situation."
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Central African Republic's interim President Michel Djotodia, the former Seleka rebel leader, has failed to control his mostly Muslim fighters, who have preyed upon the majority Christian population, unleashing tit-for-tat killings. Rights groups say both sides may have committed war crimes.
Senior UN officials warned that Central African Republic is at risk of spiraling into genocide. The United Nations estimates that 400,000 people have been displaced and 68,000 have fled to neighboring countries due to the violence.
There is a 2,500-strong peacekeeping force in Central African Republic deployed by the Economic Community of Central African States. The African Union is due to take charge of that force later this month and boost its size to 3,600 troops.
France, which already has around 400 troops based at the airport in the capital Bangui, is preparing to boost its force in its former colony to at least 1,000 soldiers.
The AP posted this raw video from CAR:
Britain's military said it was in talks with France on providing "limited logistical support" for the military intervention, amid reports that London could send a C-17 transport plane.
"Following the UNSCR (Security Council) agreement to strengthen the role of international forces in the CAR, the UK is in discussions with France about providing limited logistical support," the Ministry of Defence said in a statement.
"Sending UK combat troops is not on the table."
The UN Security Council resolution authorized the deployment of the African Union force for one year, with the operation to be reviewed after six months. It also asks Ban to set up a trust fund for voluntary contributions to finance the African force, to be known as MISCA.
"The United States is appalled by today's reports of the murder of innocent women and children outside of Bangui," State Department spokeswoman Marie Harf said in a statement Wednesday.
"This horrifying account is the latest in a string of reports that illustrate the deteriorating humanitarian and security situation in the Central African Republic (CAR) that could lead to an escalation in violence and further atrocities," she added.
Agence France-Presse and Reuters contributed to this report.