The suspect in the Dallas police sniper attacks told negotiators that he wanted to kill white people, especially white cops, after a recent spate of US officer-involved shootings of black men, the city's police chief said Friday.

Chief David Brown appealed for unity in the wake of the attacks, which left five police dead and nine wounded -- seven of them cops -- saying, "This must stop -- this divisiveness between our police and our citizens."

The suspect was killed by an explosive device detonated by police during a tense standoff after Thursday night's shooting rampage during a protest over the fatal police shootings of two black men this week in Louisiana and Minnesota, Brown said.