Rebels in Sudan's troubled Darfur region say pro-government militias have attacked the area's main town, El-Fasher.
Rebels say the Arab militia, called "Janjaweed," began looting the city's market on Monday.
A former rebel leader who is now a presidential adviser, Minni Minnawi, said the situation is critical. He said a peace deal his rebel faction signed with the government in May could be in jeopardy if such attacks are not stopped.
Minnawi's Sudan Liberation Army was the only one of three Darfur rebel groups to sign the peace deal. The agreement, however, has done little to stop the fighting.
More than two million people are estimated to have been displaced and at least 200,000 killed since Darfur rebels rose up in 2003, sparking retaliation from Janjaweed militias. The militias are accused of carrying out atrocities against villagers.