President Barack Obama said the killer who opened fire at a black church in South Carolina violated a "sacred place" in America's history and the mass shooting once again raised troubling questions about racial tension and easy access to firearms.

In what has become a grimly regular task for the president, Obama offered condolences for the grieving, a promise of help in the investigation and condemnation of senseless violence.

"Any shooting involving multiple victims is a tragedy," Obama said Thursday at the White House. "There's something particularly heartbreaking about a death happening in a place in which we seek solace and we seek peace."