Five Dallas police officers in the US have been killed and six wounded by sniper fire during protests against the shooting of black men by police, authorities say. Police are in a standoff with one armed man in a garage. Three other people have been detained. Gunfire broke out early this morning as demonstrators marched through the city. The protests were sparked by the deaths of Philando Castile in Minnesota and Alton Sterling in Louisiana. Dallas Police Chief David Brown said officers remained in a stand-off with one armed man at a garage who was firing off rounds with a rifle.