Rebel forces in the Central African Republic (CAR) have captured Bria, a key mining hub in a diamond-rich region.
The rebel coalition says it now controls at least four towns and has threatened to overthrow the government.
It wants to discuss the compliance of a ceasefire that pledged the release of political prisoners and payment for fighters who lay down their arms.
The CAR has had a series of rebellions and coups since independence in 1960.
Government soldiers are said to have tried to repel the attack on Bria, launched at dawn on Tuesday, but were later forced to retreat.
The Seleka rebel coalition – formed by factions of three groups – accuses the government of President Francois Bozize of not complying with the terms of the peace treaty signed in 2007.
It is believed to be in control of the towns of Bria, Ouadda, Sam Ouandja and Ndele, a major route linking the CAR to Sudan, Cameroon and Chad.
Military sources and the mayor of Bria have confirmed that the town's military base was taken by the rebels following the attack on Tuesday morning.
A statement sent by Seleka to news agencies outlined the group's demands and said that should they not be met, the rebels will "do everything possible to change, sooner or later, this predatory regime."
On Sunday, military sources told the news agency Reuters that a group of government soldiers sent to retake the town of Ndele was ambushed by the rebels.
In the last two weeks, the rebel alliance has been stepping up their offensive against government military positions.
Mr Bozize has been in power since leading a coup in 2003 and winning the elections in 2005 and 2011.
The 2007 accord with his government led to rebel forces being integrated into the army.
But some of the rebels have since deserted and taken up arms again.
The CAR is rich in mineral resources, including gold and diamonds, but its population is extremely poor.