Clashes between two tribes in Port Sudan on Monday left three people dead and 24 wounded, medics said, as police imposed a night-time curfew in Sudan's main economic hub.
The curfew in the Red Sea city came into effect at 5pm (1500 GMT) and would remain until 5am Tuesday, the police said in a statement posted on its Facebook page.
It did not specify when the restrictions would be lifted.
Violence erupted on Monday in Port Sudan when a prominent leader from Beni Amer tribe Al-Amin Daoud held a political rally in the city, which was opposed by members of Hadendowa tribe, the biggest in eastern Sudan, witnesses told AFP by telephone.
"Tribal clashes killed three people and wounded 24 others," a doctors committee close to Sudan's umbrella protest movement, Forces of Freedom and Change, said in a statement.
The committee did not specify the exact causes of the deaths and wounds.
A witness said earlier on Monday that a bus was set on fire during the clashes that erupted near a hospital in the downtown area of Port Sudan.
"The clashes stopped after members of the Rapid Support Force intervened," another witness said.
"The situation is still tense and RSF members are everywhere."
Tribal clashes have often rocked the northeast African country, with many resulting in deaths.
Port Sudan also witnesses regular strikes by port workers demanding better work conditions and pay.