Both rebel coalition Seleka, which has seized much of the country in the past three weeks, and leading opposition figure Martin Ziguele said that President Francois Bozize would fail to keep promises he made after talks with African Union chief Thomas Boni Yayi.

Eric Massi, a spokesman for the rebel alliance, charged that government forces were preparing an assault "to attack our positions from the rear out of Batangafo", a northern town taken by the rebels after they launched their insurgency on December 10.

"There is no longer any doubt that the sincerity of the promises made by Francois Bozize is not real," Massi told AFP.

After talks in Bangui on Sunday with Bozize, Boni Yayi said the former general was ready to negotiate with the rebels in Gabon and to form a government of national unity. He also said he would not stand for office when his current term expires in 2016.

The Seleka alliance, which has carried out a southward offensive from near the border with Chad, also accused Bozize's regime of persecuting political foes in Bangui and urged a multinational African peacekeeping force (FOMAC) to take action to stop atrocities.

"We call on the African peacekeeping forces to intervene immediately in the capital to stop the abuses and murders of prisoners, or see that they don't prevent us from doing so," Massi said.

Massi made no mention of Bozize's offer of talks, while the president did not respond to a ceasefire offer by the rebels.

Seleka began its insurgency on the grounds that Bozize's government had failed to abide by the terms of peace accords signed with various rebel groups in 2007 and 2011, which provided for disarmament and funding the reintegration of former rebels into society.

The Seleka rebels have taken several major towns, including the diamond-mining hub of Bria, and were on Monday within 160 kilometres (100 miles) of the capital.

Central Bangui was lively on Monday, as workers in the state and private sectors queued outside banks to get their monthly pay. Troops were deployed in force in the city for the first time since the crisis began.

FOMAC troops have deployed to Damara, the last strategic town between rebel positions and the capital.

Echoing the rebels' scepticism, leading opposition figure Ziguele -- a former prime minister under Ange-Felix Patasse, the president Bozize toppled in a 2003 coup -- said he had little faith in Bozize's pledges.

"The problem is Mr. Bozize's promises. He makes promises and doesn't keep them," Ziguele said, accusing the president of having a "credibility problem".

"What concession has he made? Not to run in 2016? The constitution clearly says he doesn't have the right to do so!"

Ziguele said there was no point in holding talks on a national unity government.

"This is not the debate," he said. "This is not the time for a redistribution of posts. We should review the structures of government, we need structural solutions to the major problems of governance. There should be dialogue."

A government minister meanwhile warned that unilateral pressure on Bozize was counter-productive and could lead to a destabilising coup.

"The president has made concessions, he has given every guarantee, but the pressure must not be unilateral," said Territorial Administration Minister Jose Binoua.

"Unilateral pressure will create a hardening among people in the regime.... This could lead to a palace revolution."

Bozize has appealed for help from former colonial power France, which has propped up previous regimes in the chronically unstable country of five million people, but Paris has refused to intervene.

"The commitments made yesterday by President Francois Bozize go in the right direction," French Foreign Minister Laurent Fabius said Monday in a statement.

"The priority more than ever is dialogue and an end to hostilities," he added. "I urge all parties to start negotiations without delay."

Almost 600 French troops are permanently stationed in Bangui, but Paris has announced that their sole task is to ensure the safety of an estimated 1,200 French nationals.