The United Nations is evacuating its non-essential staff from the Central African Republic as rebels advance towards the capital, Bangui.
The US has urged its nationals to leave.
France has ordered tighter security of its embassy in Bangui after it was attacked by protesters.
A government minister has called for French soldiers stationed there to intervene as rebels closed in on the capital having passed the last major town to the north.
The appeal for help came as hundreds of people protested outside the French Embassy in Bangui, throwing stones at the building and tearing down the French flag in anger at the rebel advance.
France maintains a presence in CAR to protect its interests and French citizens, not the government of President Francois Bozize, French President Francois Hollande said.
The UN criticised the rebel advance.
UN Secretary-General Ban Ki-moon's spokesman, Martin Nesirky, issued a statement saying Mr Ban "strongly condemns the armed attacks on several towns in the Central African Republic perpetrated by the coalition of rebel groups 'SELEKA'”.
"These developments gravely undermine the peace agreements in place and the efforts of the international community to consolidate peace in the Central African Republic," he said.
The rebel push through a string of towns in recent weeks has highlighted the fragility of the land-locked nation, which has rich deposits of uranium as well as gold and diamonds but has been largely unstable since independence from France in 1960.