Two associations representing police officers urged calm following the killing of five officers by gunmen in Dallas Thursday night. At the same time, the association representing African American newspapers called on President Barack Obama to appoint a special prosecutor to investigate the recent shootings of two black men by police.

Details were still scarce Friday morning about what motivated perhaps as many as four gunmen to open fire on Dallas police officers guarding a Black Lives Matter protest. In a statement, the National Sheriffs' Association said the attack "is probably the most deadly ambush and assassination of law enforcement officers in U.S. history in a coordinated attack."

The association called for calm, asking for patience for the justice system process.

"It must be given the chance to work no matter how angry people may be," NSA said. "Taking the law into one's own hands will not solve the problems we face. Everyone in this country must now come together and work together to resolve these issues."

The International Association of Chiefs of Police weighed in with a tweet: "The thoughts & prayers of the members of @TheIACP are with the officers, families & community impacted by the horrific events in Dallas."

Early news reports indicate the shooters may have been seeking revenge for the shooting deaths of two African American men by police in Louisiana and Minnesota. A few hours before the shooting, IACP also commented on those deaths, calling the loss of any life a tragedy and offering condolences to the families of the men who were killed.

"We encourage everyone, including our elected officials, to reserve judgment while expedited yet thorough investigations proceed," the association said. "Public statements that presuppose guilt, inflame public opinion or prejudice investigations serve no useful purpose."

That same day, the National Newspaper Publishers Association—which represents African American newspapers—called on Obama and U.S Attorney General Loretta Lynch to appoint a special prosecutor to investigate the police shootings.

"The killings of African Americans in Louisiana and Minnesota during the past 72 hours represent an escalating national pattern of fatal police killings that appear to be racially motivated," NNPA CEO Benjamin Chavis said. "These incidents are not isolated local tragedies, but are the terrible growing manifestations of a deadly national system of racism in the criminal justice system that needs to be effectively challenged and changed."

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