Dallas Police Chief David Brown said the sniper fired "ambush-style" upon the officers.
The shooter has been identified as Micah Johnson, 25, according to The Associated Press.
Police would not confirm during a Friday morning news conference if other suspects are in custody or being sought. It is believed that the shooter acted alone. A search of his home found bomb-making materials and weapons.
>>Photos: Officers shot in Dallas, Texas
The gunfire broke out around 8:45 p.m. Thursday. Video from the scene showed protesters marching along a street in downtown Dallas when the shots erupted and the crowd scattered, seeking cover.
A witness told KTVT, "Whoever was shooting had an assault rifle — and I know guns. The shots were in rapid succession."
Scores of police and security officers were on hand. Police and others hunched behind cars outside a parking garage. Officers with guns drawn were running near and into the parking garage as police searched for the shooter.
The Associated Press contributed to this report.
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