African Union observers say Sudan has failed to meet a deadline to abide by a cease-fire and stop attacking rebels in the western Darfur region.
AU officials reported fresh fighting Sunday, after mediators in Nigeria threatened to take Sudan and the rebels to the U.N. Security Council.
Unknown gunmen also fired Sunday at an African Union helicopter in Darfur. There are no reports of casualties.
Sudanese Foreign Minister Mustafa Osman had earlier announced an immediate halt to all military operations in Darfur and asked the United Nations to make the same demand of the rebels.
But a rebel spokesman told the Reuters News Agency that Sudan has failed to keep earlier promises to stop attacks.
Fighting between largely Arab pro-government militias and non-Arab rebels in Darfur has left tens of thousands dead, including many civilians.
Some information for this report provided by AP and Reuters.