CAR crisis: Gunfire and explosions heard in Bangui
Fresh clashes have broken out in Bangui, the capital of the Central African Republic (CAR), amid growing tension between rival militias.
Heavy gunfire and explosions were heard throughout the night and again on Thursday. Shops have shut and residents are staying indoors.
The Red Cross says its workers have been unable to respond to calls for help after being threatened.
At least 5,000 people have been killed in religious violence in CAR this year.
A deadline for the resignation of interim President Catherine Samba Panza - issued by a Christian-dominated militia - expired this week.
The latest clashes are the fiercest since a UN force took over peacekeeping duties last month.
Red Cross threats
According to an official from the UN force quoted by the AFP news agency, the violence was sparked this week by a grenade attack that injured several pedestrians in Bangui.
The attacker, riding a motorcycle, "was chased, apprehended and killed by unidentified men," the official is quoted as saying.
Further clashes then erupted in the city's KM5 district.
The BBC's Laeila Adjovi in Bangui says the city's streets are empty, shops, fuel stations, and humanitarian agencies are closed.
Militia roadblocks have been reported in some parts of the city, as French army helicopters fly overhead, she says.
At least 5 people were confirmed to have been killed in clashes on Wednesday, but after a night of heavy fighting, the Central African Red Cross confirmed to the BBC that they have been unable to access areas to assist wounded and retrieve bodies.
The Red Cross have also confirmed that their staff have been directly threatened.
"The threats must stop, said Jean-François Sangsue, the head of the ICRC delegation in Bangui in a statement released on Thursday.
"We are asking the population to facilitate the work of Red Cross volunteers. If the threats continue we will be obliged to cease all relief activities, leaving many victims to fend for themselves," he said.
CAR has suffered ethnic and religious unrest for more than a year since mainly Muslim Seleka rebels seized power in the majority Christian country.
Muslim rebel leader Michel Djotodia resigned in January under diplomatic pressure, but violence between Christian and Muslim militia groups has continued.
Both groups have been accused of targeting civilians. Thousands have been killed and tens of thousands more have fled the country.
The UN says that about 1.3 million people - a quarter of the population - are in need of aid.