Micah Xavier Johnson, who was involved in the killing of five US police officers in Dallas before himself being killed by police, was a US army veteran who had served in Afghanistan.

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During negotiations with police, Johnson said he was upset about the recent police shootings of black people, Police Chief David Brown said.

"The suspect said he was upset at white people. The suspect stated that he wanted to kill white people, especially white officers," Mr Brown told a news conference.

Johnson's Facebook profile photograph showed him giving a raised fist "black power" salute associated with the Black Panther Party movement, a radical political organisation that emerged during the 1960s in response to police brutality in California.