Rebels in the Central African Republic said they are ending a cease-fire after the government failed to meet a series of recent demands.
Eric Massi, a spokesman for the Seleka rebel coalition said on Wednesday that the rebel ultimatum has "expired" and hostilities may resume.
The rebels already went on the offensive last week, taking control of three southeastern towns. They are also holding five ministers who had joined the government from rebel ranks as part of a January peace deal.
Seleka has accused the government of not living up to that accord, and demanded the departure of South African troops protecting the government in the capital, Bangui.
The rebels launched their initial offensive in December and came less than 100 kilometers of Bangui.
Seleka unites at least three rebel groups in the north that say the government failed to implement peace deals signed in 2007 and 2011 that included paying rebel fighters and integrating them into the army.
On Sunday, the United States said it was deeply concerned by the deterioration in the CAR's security situation. It called on President Bozize and the Seleka rebel coalition to cease hostilities immediately and implement the provisions of the Libreville agreement.