African Union to boost Central African Republic force
The African Union has authorised increasing the number of troops deployed in the Central African Republic to 6,000, say officials.
CAR fell into sectarian conflict after rebel leader Michel Djotodia ousted President Francois Bozize in March.
The AU troops are attempting to restore order and disarm the militia which now control much of the country.
France's defence minister has warned the country is facing "the early beginnings of a humanitarian crisis".
Jean-Yves Le Drian was in the CAR capital, Bangui, on Friday to meet some of the 1,600 French troops deployed there, and to hold talks with officials.
He said the "spiral of confrontation has abruptly worsened".
France is the former colonial power in CAR, which is one of the world's poorest countries. Two French soldiers have died in fighting.
El Ghassim Wane, director of the AU's Peace and Security Department, (PSC) told Reuters that approval had been given to increase troop numbers to 6,000 "depending on the needs".
He said the PSC would review the situation again in three months.
Mr Djotodia, formerly the leader of the mainly Muslim Seleka rebel alliance, installed himself as the first Muslim leader in the Christian-majority country in March.
Seleka has now been officially disbanded but its fighters remain at large and are accused of atrocities against Christians.
Christian self-defence militias have since sprung up and the country has spiralled into sectarian conflict.
More than 500 people have been killed in the capital alone in the past week and an estimated 10% of the CAR's 4.6 million people have fled their homes.
Intense clashes were reported in several districts of Bangui on Friday. French soldiers were involved in at least one exchange of fire with former rebels.
"It was horrible. There was firing everywhere," a Bangui resident who gave her name as Jennifer told the AFP news agency.
"I don't know who it was, I didn't try to see if it was Seleka, the French or someone else. It lasted a long time."
The UN reports that 27 Muslims were killed in the village of Bohong, not far from CAR's western border with Cameroon, on Thursday by the anti-Balaka Christian militia.
"The situation is also tense in several towns, including Bouca, Bossangoa and Bozoum, where a vicious cycle of attacks and reprisals continues," the UN's human rights office said.
CAR Prime Minister Nicolas Tiangaye has warned there is an urgent need to disarm all sides.
"Religious communities that have always lived together in perfect harmony are now massacring each other," the Associated Press quotes him as saying.
"The situation must be stopped as soon as possible."
Save the Children has said it is treating children as young as three for machete and gunshot wounds, and has urged the UN to deploy in the more remote regions.
The charity also said some 6,000 children had been conscripted into armed groups in CAR.
The first of 850 Burundian troops operating under the AU mission flew into Bangui on Friday on a US military aircraft.
Their commander, Lt-Col Potien Hakizimana, said their mission included "ensuring the disarmament of militia forces, securing the population and property, and help restore authority over the entire country".
A plane carrying 77 tonnes of aid was due to land in Bangui on Friday afternoon, but aid agencies say the humanitarian situation is rapidly deteriorating.
In an open letter published on Thursday, MSF criticised "the unacceptable performance of the United Nations humanitarian system in the Central African Republic over the last year".
MSF's general director Arjan Hehenkamp told the BBC on Friday that the UN appeared to have gone into "security lockdown" despite the ongoing crisis.
"There needs to be a dramatic scale up of assistance and presence throughout the country in order to give confidence to the population, but primarily to give assistance to the population."
An estimated 40,000 people have gathered at Bangui's airport. Aid workers there say there is no sanitation, no shelter from heavy rain, and that disease is spreading.
One woman told the Associated Press she had been there with her 10 children for a week without finding food.
"The kids are so hungry - they keep asking for food but we have nothing," she said.
The UN's humanitarian co-ordinator in Bangui, Kaarina Immonen, acknowledged that there had been problems getting aid to people at the airport, partly because it was such a strategically important location.
She told the BBC that aid distribution was now under way, but taking place a short distance from the airport, to ensure the safety of those in need.