West Columbia, South Carolina (CNN) Hillary Clinton said Thursday that the United States needs to confront "systemic racism" in its law enforcement efforts — declaring again that "black lives matter."

The Democratic presidential front-runner's comments during a Thursday morning campaign event are her latest effort -- just days after making the same comment in a Facebook chat -- to embrace the outrage over African-Americans' deaths in police custody and in racially-motivated shootings.

"I think we first have to acknowledge and believe that black lives matter. This is not just a slogan, this should be a guiding principle," Clinton told the crowd of 400 at the Brookland Baptist Church in West Columbia.

She was asked about the "epidemic proportions" of African-Americans who have died in police hands -- and she mentioned Sandra Bland, a Texas woman who died in jail after she was arrested following a traffic stop.

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