DALLAS (AP) -- Snipers opened fire on police officers in the heart of Dallas, killing five officers and injuring six others during protests over two recent fatal police shootings of black men.

Three people are in custody and a fourth suspect was exchanging gunfire with authorities in a parking garage downtown, Dallas Police Chief David Brown said early Friday morning.

The suspect is not cooperating and has told negotiators he intends to hurt more law enforcement officials, the chief said.

The gunfire broke out around 8:45 p.m. Thursday while hundreds of people were gathered to protest fatal police shootings this week in Baton Rouge, Louisiana, and suburban St. Paul, Minnesota. Brown told reporters the snipers fired "ambush style" upon the officers. Mayor Mike Rawlings said one member of the public was wounded in the gunfire.

Protests were also held in several other cities across the country Thursday night after a Minnesota officer on Wednesday fatally shot Philando Castile while he was in a car with a woman and a child. The aftermath of the shooting was livestreamed in a widely shared Facebook video. A day earlier, Alton Sterling was shot in Louisiana after being pinned to the pavement by two white officers. That, too, was captured on a cellphone video.

Video footage from the Dallas scene showed protesters were marching along a street in downtown, about half a mile from City Hall, when the shots erupted and the crowd scattered, seeking cover.

Brown said that it appeared the shooters "planned to injure and kill as many officers as they could."

The search for the shooters stretched throughout downtown, an area of hotels, restaurants, businesses and some residential apartments. The area is only a few blocks away from Dealey Plaza, where President John F. Kennedy was assassinated in 1963. Some of the injured officers were taken to Parkland Hospital.