Rebels continued their advance on Saturday, seizing the city of Sibut, 185 kilometers (114 miles) from Bangui, the capital, a government official confirmed.
Sibut, a key transportation hub, fell without a shot being fired because the Central African Republic army and forces from neighboring Chad had pulled back to Damara, 75 kilometers (46 miles) from Bangui on Friday, said Minister of Territorial Administration Josie Binoua.
The telephone lines to Sibut have been cut, making it difficult to check the situation with local residents.
The news of the rebels taking Sibut comes as regional African countries have agreed to send more forces to support the government of President Francois Bozize.
Talks between the rebels and the Bozize government are planned to start next week in Gabon.
Representatives from the 10-nation Economic Community of Central African States agreed at a meeting in Gabon Friday to send forces to CAR, but did not did not specify how many troops would be sent or how quickly the military assistance would arrive.
As fears mounted that the rebels would attack the capital of 600,000, Bozize pleaded for international help. But former colonial power France said its forces in the country are there to protect French interests and not Bozize's government. About 200 French soldiers are already in the country, providing technical support and helping to train the local army, according to the French defense ministry.
Paris is encouraging peace talks between the government and the rebels, with the French Foreign Ministry noting in a statement that negotiations are due to "begin shortly in Libreville (Gabon)." But it was not immediately clear if any dates have been set for those talks.
The ongoing instability prompted the United States to evacuate about 40 people, including the U.S. ambassador, from Bangui on an U.S. Air Force plane bound for Kenya, said U.S. officials who insisted on anonymity because they weren't authorized to discuss the operation.
The United States has special forces troops in the country who are assisting in the hunt for Joseph Kony, the fugitive rebel leader of another rebel group known as the Lord's Resistance Army. The U.S. special forces remain in the country, the U.S. military's Africa Command said from its headquarters in Stuttgart, Germany.
The evacuation of the U.S. diplomats came after criticism of how the U.S. handled diplomatic security before and during the attack on its consulate in Benghazi, Libya, on Sept. 11. The ambassador and three other Americans were killed in that attack.
French diplomats have remained in Bangui despite a violent demonstration outside its embassy earlier this week. Dozens of protesters, angry about France's lack of help against rebel forces, threw rocks at the French Embassy in Bangui and stole a French flag. French Foreign Minister Laurent Fabius spoke via phone with Bozize, asking him to take responsibility for the safety of French nationals and diplomatic missions in Central African Republic.
This landlocked nation of 4.4 million people has suffered decades of army revolts, coups and rebellions since gaining independence in 1960 and remains one of the poorest countries in the world. The current president himself came to power nearly a decade ago in the wake of a rebellion in this resource-rich yet deeply poor country.
Bozize's government earlier reached out to longtime ally Chad, which pledged to send 2,000 troops to bolster Central African Republic's own forces.
The rebels behind the most recent instability signed a 2007 peace accord allowing them to join the regular army, but insurgent leaders say the deal wasn't fully implemented. The rebel forces have seized at least 10 towns across the sparsely populated north of the country. Residents in the capital now fear the insurgents could attack at any time, despite assurances by rebel leaders that they are willing to engage in dialogue instead of attacking Bangui.
The rebels have say they are fighting because of their "thirst for justice, for peace, for security and for economic development of the people of Central African Republic." The rebels also are demanding that the government make payments to ex-combatants.
Despite Central African Republic's wealth of gold, diamonds, timber and uranium, the government remains perpetually cash-strapped.
The United Nations Security Council condemned the violence and reiterated its demand that the armed groups "immediately cease hostilities, withdraw from captured cities and cease any further advance towards the city of Bangui."