The US says it has evacuated its embassy in the Central African Republic as rebels threaten to advance towards the capital, Bangui.
The state department said it had not broken off diplomatic ties with the government but warned US citizens not to travel to CAR during the unrest.
Earlier, CAR President Francois Bozize appealed to the US and France to help block the rebel advance.
The UN has said it is evacuating its non-essential staff from the country.
US state department spokesman Patrick Ventrell said the embassy had suspended operations and that the ambassador and other staff had left the country on Thursday.
"This decision is solely due to concerns about the security of our personnel and has no relation to our continuing and long-standing diplomatic relations with the CAR," he said in a statement.
The BBC's Junior Lingangue in Bangui says resident are stockpiling food amid fears that the rebels - known as the Seleka coalition - could launch an assault in the next few days.
On Sunday, the rebels captured the northern city of Bambari, the third largest in the country, having earlier seized the rich diamond mining area around Bria.
On Wednesday, protesters in Bangui attacked the embassy of former colonial power France, accusing Paris of abandoning them.
France has about 200 soldiers based in CAR and stepped up security at its embassy after the attack.
President Bozize apologised for the incident and appealed for "our French cousins" and the US "to help us to push back the rebels".
However, French President Francois Hollande said Paris would not intervene in its former colony.
"If we have a presence, it's not to protect a regime, it's to protect our nationals and our interests and in no way to intervene in the internal business of a country, in this case the Central African Republic," he said. "Those days are over."
Seleka, which is made up of breakaway factions from three former armed groups, accuses Mr Bozize of failing to honour a 2007 peace deal, under which fighters who laid down their arms were meant to be paid.
The rebels have pledged to depose Mr Bozize unless he negotiates with them.
They began their campaign a month ago and have taken several towns in their push towards the capital.