Gunfire broke out near key military installations in the largest city of Sudan's Darfur region on Thursday after overnight battles killed a local bandit, residents and other sources said.
The fighting came as the United Nations peacekeeping chief Herve Ladsous visited Darfur, where there has been an upsurge of violence this year.
Continuous gunfire could be heard over the telephone as an AFP correspondent spoke with a local resident of Nyala, Sudan's second-largest city, on Thursday.
The shooting appeared to be coming from the downtown area where security forces headquarters are located, the resident said.
Fighting began on Wednesday night when a carjacker was killed, leading his group to retaliate against government forces, sources familiar with the incident said.
After the initial battle, the security forces reinforced their compounds in the city, the sources said.
"There were huge explosions heard, and gunfire," during the Wednesday night clash, one resident said.
A United Nations panel of experts said in February it had collected testimonies of insecurity, including "growing crime inside towns such as Nyala".
Rebels have been fighting for 10 years in Sudan's far-western Darfur.
While the worst of the violence has long passed, instability has been complicated by inter-Arab fighting, kidnappings, carjackings and other crimes, many suspected to be the work of government-linked militia and paramilitary groups.
Ladsous was in transit through Nyala's airport early on Thursday on his way to Khartoum at the end of his visit, a UNAMID spokesman said.