Monday, the government and an opposition bloc signed a UN-brokered peace deal. But Tuesday, Islamist hard-liners said they would continue to fight.
Fighting flared this week in an oil-rich flashpoint in central Sudan.
Ongoing violence may impede a runoff between President Robert Mugabe and the opposition's Morgan Tsangirai.
Security has improved slightly in parts of Sudan's troubled western region, but only 9,000 of the 26,000 peacekeeping troops have been deployed so far.
President Mugabe's electoral commission on Sunday delayed a recount of the March 29 vote, raising concerns of vote rigging.
Five things we think you'll like this week, including a Domingo concert without the expensive seats, the return of Botswana's answer to Miss Marple, and a TV show of dance choreography inside national parks.
The country's electoral commission said releasing results from the March 29 presidential vote would be 'dangerous' as international efforts for release of poll widened.