Dallas police exchanged gunfire early Friday with a suspect in a deadly shooting that has killed four officers who warned negotiators there were "bombs all over the place" in downtown Texas, officials said.

"The suspect that we are negotiating with that has exchanged gunfire with us over the last 45 minutes has told our negotiators that the end is coming, and he is going to hurt and kill more of us, meaning law enforcement. And that there are bombs all over the place in this garage and in downtown," Police Chief David Brown told reporters.

"So we are being very careful in our tactics so we don't injure our citizens in Dallas as we negotiate further."

The man suspected of opening fire on police officers in Dallas, killing five and wounding seven others, was identified as 25-year-old Texas resident Micah Johnson.

Johnson lived in the Dallas suburb of Mesquite, CBS News and NBC News reported. He was killed in a tense showdown with police after the shootings, which also left two civilians wounded.

CNN, citing an unnamed law enforcement official said Johnson had no criminal record or known ties to extremists.

The network broadcast what it said was a photograph of the suspect, a black man with a short beard shown with his fist raised and wearing an African-style print tunic.

Johnson served in the US Army Reserves until April 2015, ABC News reported. Unnamed defense officials told the network he was trained as a carpentry and masonry specialist.

Earlier, Dallas police said the main shooting suspect had told negotiators he was not affiliated with any groups.

The suspect told negotiators he was upset about the recent fatal police shootings of black men, and wanted to kill white people -- specifically, white cops.