Rebels in Central African Republic have dismissed the president's offer to form a national unity government.
"We don't believe in [Francois] Bozize's promises," rebel spokesman Eric Massi told the BBC.
He accused the security forces of attacking members of ethnic groups seen as rebel sympathisers - the government has previously denied such claims.
The rebels have seized several towns as they advance on the capital, Bangui, in recent weeks.
Mr Massi, speaking by telephone from Gabon, said that African peacekeepers must be deployed to protect northerners living in Bangui.
"If they don't do that, we will protect them ourselves," he said.
He accused the authorities of handing out machetes and kalashnikov rifles to civilians and said more than 400 people had disappeared in recent weeks.
Government troops have pulled back to Damara, 75km (48 miles) from the capital, in the face of the rebel advance.
The African Union has warned the Seleka rebel alliance they would face sanctions if they seized power, the AP news agency reports.
After talks with African Union chairman Thomas Boni Yayi on Sunday, President Bozize said he would form a coalition government and step down when his term ends in 2016.
He also said he was ready to attend peace talks in Gabon "without condition and without delay".
More troops from the Central African Multinational Force (Fomac) arrived in CAR on Saturday to reinforce a contingent already there.
More than 100 French paratroopers have also been sent in. However, France, the former colonial power, insists they are only there to secure its nationals - not to save Mr Bozize's government.
A senior UN official told the BBC that all its international staff had been evacuated to neighbouring Cameroon.
The US has also evacuated its embassy in Bangui.
BBC West Africa correspondent Thomas Fessy says there was no fighting when rebels entered Sibut on Saturday.
The city is about 150km (95 miles) from Bangui.
Government troops and Chadian soldiers deployed as a buffer force had left their position hours before and a rebel spokesman said they took over the city because it was abandoned.
Seleka - an alliance of three separate groups - accuses Mr Bozize of failing to honour a 2007 peace deal under which fighters who laid down their arms were meant to be paid.
They began their campaign a month ago and have taken several key towns and cities including Bambari and the diamond centre of Bria in their push towards the capital.
In Bangui, residents have reported sharp rises in staple food prices as the rebels draw closer.