The fighting, which escalated over the weekend, has also forced thousands of people to flee their homes, said the UN and a local committee of doctors on Tuesday.
“The number of deaths has risen to 56 and more have been injured,” the UN humanitarian coordination office said. “People are fleeing into neighboring Chad.”
Clashes erupted between Arab tribes and the non-Arab Masalit ethnic group after unknown assailants shot at Masalit tribesmen on Saturday evening, killing two and injuring as many.
Heavy weaponry and rocket-propelled grenades have been used in the clashes.
According to the UN, there have also been attacks on civilians, including women and children, as well as on humanitarian facilities.