The United States evacuated its embassy in the Central African Republic and temporarily halted its operations, amid security fears after rebels seized large swathes of the country.

The State Department said it had not broken off diplomatic ties with the beleaguered government in Bangui, but warned US citizens not to travel to the mineral-rich but chronically unstable country while unrest continues.

"Ambassador (Lawrence) Wohlers and his diplomatic team left Bangui today along with several private US citizens," a statement said. Separately, a US official told AFP the team flew out of Bangui at 0000 GMT Friday.

"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," the State Department said.

In a separate travel warning issued to US citizens, the department said: "As a result of the deteriorating security situation, the US Embassy in Bangui suspended its operations on December 28, 2012.

"The Department of State warns U.S. citizens against all travel to the Central African Republic," it said.

"US citizens who have decided to stay in CAR should review their personal security situation and seriously consider departing."

Washington's decision comes amid mounting fears in the Central African Republic's capital that President Francois Bozize's government is facing defeat by an advancing army of rebel fighters.

The United Nations has also pulled non-essential staff out of the country, which has a history of violent unrest, and former colonial power France has ordered its military to step up security around its Bangui embassy.

A rebel coalition known as Seleka -- which means "alliance" in the country's Sango language -- has seized four regional centers, including a diamond mining hub, since its fighters took up arms on December 10.

Bozize's troops have fallen back from the rebel advance in disarray and he has appealed for US and French help.