The United Nations is said to be pulling out all non-essential staff from the Central African Republic in response to Seleka rebels advancing to within 75km of the capital, Bangui.
Residents of Bangui shut their offices, schools and shops on Saturday, as the Seleka movement - an alliance of three rebel groups - seized control of Bossembele, a town 160km northwest of Bangui late on Friday.
"We have taken Bossembele. We are now 100km from Bangui on this [northwestern] front."
- Seleka spokesman Eric Massi
A spokesman for rebel coalition, which accuses President Francois Bozize of breaking a January peace agreement to integrate its fighters into the army, claimed a second column was around 30km from the capital to the northeast.
Local residents reported fierce fighting in Bossembele, which is home to a major military barracks, and at least one said rebels had captured the town. It was not immediately possible to confirm this with government officials.
"We have taken Bossembele," Seleka spokesman Eric Massi said by telephone from Paris. "We are now 100km from Bangui on this front."
Seleka, a loose umbrella group of fighters, fought its way to the gates of the capital last year after accusing Bozize of failing to honour an earlier peace deal to give its fighters cash and jobs in exchange for laying down their arms.
It now says it has lost faith in Bozize, who seized power in the former French colony in a 2003 coup, and will topple him.
Speaking to Al Jazeera from Paris, Lydie Boka, an Africa analyst and director of Strategic Co., said the two key players at this moment are Chad and South Africa.
"South Africa clearly wants to play a bigger role in Africa because it is afraid of too much French influence as it has commercial interests there. It has been supporting the Bozize regime since 2007. So, whether rebels will take the risk of clashing with well-trained South African forces, remains to be seen," Boka said.
"Chad issued a warning to the rebels in January to not cross the red line of Damara, which is 50km from the capital. Chad this time had been silent about that red line but its forces are at the entrance of Bangui, and we'll see whether they will let the rebels go through, because Chad is potentially also facing a rebellion."
The violence is the latest in a series of rebel incursions, clashes and coups that have plagued the landlocked nation in the heart of Africa since its independence in 1960.
Residents in Bossembele reported gun battles between rebels and government forces, particularly around the military barracks on the southern route from the town.
"The town has fallen to the rebels," said Jean-Claude Sambia. "They control the town now and are everywhere."
The Seleka column had advanced southwards a day after capturing Bozize's hometown of Bossangoa, a major garrison town 300 km northwest of Bangui.
In the riverside capital, shops reopened and traffic returned to the streets after news on Friday of another rebel column less than 75km to the northeast had sown panic.