France steps in as violence in the troubled former colony claims more than 100 lives. Britain pledges to support the operation with a military transport plane.
About 650 French soldiers are in the Central African Republic (CAR) and that number is set to double as reinforcements are flown in from neighbouring countries, the French government said.
Speaking hours after securing UN backing for the mission on Thursday, French President Francois Hollande said the operation would be limited in time, with the aim of handing over to African forces as soon as possible.
French Foreign Minister Laurent Fabius said French forces would initially focus on securing Bangui and roads leading to neighbouring Chad and Cameroon.
They would also deploy with African forces to other towns including Bossangoa, about 300 km north of the capital, which witnesses said had come under heavy fire from former rebels on Thursday.
Early on Thursday, hours before the UN Security Council granted its approval, French forces killed an unknown number of fighters near the airport in the capital Bangui.
An army spokesman said: “Armed gunmen in pick-up trucks fired on French positions at the airport yesterday morning. We fired back. The pick-up was destroyed and the gunmen were killed.”
The foreign secretary, William Hague, said an RAF C-17 plane will make three flights transporting French equipment to the country.
The deployment of the plane comes after the UK announced £10m in aid last month, on top of £5m contributed in July, making the country one of the largest donors of humanitarian assistance to the CAR.
France’s intervention comes just months after it sent troops into Mali to stop Islamist rebels taking the capital Bamako.
Local witnesses said more than 100 people died in a night of fighting in the capital on Thursday.
And at least 39 people were killed overnight and on Friday, the Archbishop of Bangui said.
Dieudonne Nzapalainga said nine people had been executed in the Boeing neighbourhood, near the airport, while another 30 bodies had been brought to the mosque in the PK5 neighbourhood.
The CAR has been sliding towards anarchy since mainly Muslim Seleka rebels from the north of the country seized Bangui in March.
Christian militiamen and fighters loyal to ousted president Francois Bozize are fighting the rebels, and there have been outbreaks of sectarian violence.
Channel 4 News journalist and cameraman Stuart Webb sent these photographs of victims of the conflict, including six-year-old Celine (top), who lost an arm when Seleka rebels attacked her village.
A father cradles his baby after the child was shot in the buttocks as the pair ran through the bush trying to escape the same attack. The baby’s mother and three siblings died at the hands of the rebels.
Webb said local medical facilities are failing to cope with the crisis, with an acute lack of supplies and qualified staff.
Injured fighters demand treatment in clinics – then steal the mattresses from the hospital beds when they leave. The presence of armed men means local civilians are too afraid to seek medical help.