The UN Security Council and Secretary-General Ban Ki-moon have expressed strong concern at reports that rebels are advancing toward the capital of Central African Republic and demanded an immediate halt to the offensive.
In a press statement after a briefing Friday evening, the council warned against attacks on civilians and urged respect for human rights, saying violators must be held accountable and could be prosecuted by the International Criminal Court.
In separate statements, the council and the UN chief condemned the Seleka rebel movement for undermining stability and abandoning a January peace agreement and urged implementation of the accord.
Al Jazeera's James Bays, reporting from UN headquarters in New York, said: "The UN and the UN secretary general had said all sides must respect humanitariarn law and that all sides should respect previous commitments."
Our correspondent, said late on Friday that local people had been reporting an "atmosphere of fear" in the area around the capital Bangui.
"At first light, rebels could enter the capital," said Bays.
Earlier on Friday, the rebels reached the outskirts of Bangui after seizing the nearby town of Damara, rebels and military officials said. The assault came a day after the fighters has rejected a peace offer from the president.
A rebel spokesman said on Friday they had moved past Damara, about 75km from Bangui, and had advanced to within 22km of the riverside capital, sending a sense of fear among the residents.
"Our objective is to take Bangui today," Nelson Ndjadder, spokesman for the CPSK faction of the Seleka rebels, told Reuters by telephone from Paris.
"We have 2,000 men on the ground and some have slipped into the capital."
By seizing Damara the rebels had crossed the boundary line drawn by regional forces in January, when the same rebel group threatened to take the capital if their demands were not met.
The rebels seized more than 10 towns across the sparsely populated north of the deeply impoverished country in its January offensive since they took up arms in December last year.
They had stopped their advance on the capital after a peace deal was signed with President Francois Bozize in Libreville, the capital of Gabon.
A spokesman for France's foreign ministry confirmed that the rebels have advanced to within "a few kilometres" of the capital.
Military officials said the rebels had also captured Bozize's hometown of Bossangoa, about 300km from Bangui, one of the largest towns in the country's north and a barracks for the republican guard.
"It is serious. Bossangoa has fallen," said one senior Central African Republic defence official.
National radio announced on Friday afternoon that President Bozize had returned from a meeting in South Africa.
The country's prime minister, meanwhile, had sought refuge at a military base for regional forces known as FOMAC, according to soldier Jean-Pierre Sadou.
A government minister, who asked not to be identified, said Bozize had instructed his cabinet to seek safety.
Seleka resumed hostilities this week, accusing President Bozize, who seized power in a 2003 coup backed by Chad, of breaking the January peace deal.
The rebels have accused the government of not honouring another deal signed in 2007, which allowed them to join the regular army.
In Bangui, panicked residents ran through the streets, shops closed and schools sent home pupils after national radio announced the rebel advance.
A regional peacekeeping force from neighbouring central African states had established Damara as a 'red line' for the Seleka not to cross when they bore down on the capital last year.
However, residents in Damara said the peacekeepers had simply stood aside to allow the rebels to take the town.
A senior official with the regional peacekeeping force said their mandate did not allow them to intervene unless attacked.
The United Nations Security Council scheduled emergency closed consultations on Friday to discuss the latest developments in the country.
The 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.