Fourteen people have been arrested over deadly tribal clashes in Aswan that have killed 25 since Friday.
They were detained on Monday morning as police fought with crowds that had blocked a main road with burning tires, Al Ahram Arabic news website reported.
A mission from Al Azhar, the highest seat of Sunni Islam, will travel to the area on Monday in a bid to quell the violence.
Interim Prime Minister Ibrahim Mahlab and Interior Minister Mohamed Ibrahim travelled to Aswan on Saturday to mediate a truce. Mahlab promised a fact-finding mission to investigate how the violence erupted and foster reconciliation.
The two sides exchanged gunfire and hurled petrol bombs, setting fire to several houses and shops before police and troops were able to briefly end the violence on Saturday morning.
Nubians torched carts belonging to the Bani Helal tribe, Al-Ahram reported.
Police said the tensions began on Wednesday between an Arab clan, Bani Helal, and a Nubian tribe, Daboudiya, over the harassment of a girl and offensive graffiti.
A brief truce was reached with the help of police before a failed reconciliation meeting on Friday ended in a gun battle.
Most deaths were reportedly of Bani Helal members.
Revenge killings are commonplace in southern Egypt, often over a perceived loss of honour.
The army said the strife showed "signs of involvement" by the Muslim Brotherhood.
The Islamist group consistently denies any links to violence and says it is peaceful.
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