US Senators and members of Congress congregate for prayer circle honoring SC shooting victims outside US Capitol in Washington, June 18, 2015. [Photo/Agencies]

"I've had to make statements like this too many times," the president said.

The president acknowledged there is scant sentiment within the Republican-controlled Congress for stricter gun controls, saying he recognizes "the politics in this town foreclose a lot of those avenues right now." A federal universal background bill couldn't muster the 60 votes necessary even in a Democrat-controlled US Senate in the months after the 2012 shooting rampage in Newtown, Connecticut.

But Obama held out hope for an eventual shift in attitudes.

"At some point it's going to be important for the American people to come to grips with it, and for us to be able to shift how we think about the issue of gun violence collectively," he said.

Obama said the shooting in a black church also raised questions "about a dark part of our history" of racism, but he said the broad-based outpouring of grief at the tragedy shows "the degree to which those old vestiges of hatred can be overcome."

Obama, accompanied by Vice-President Joe Biden, said that he and Biden had spoken with Charleston Mayor Joseph Riley and other local leaders to express their condolences. Michelle Obama and daughter Malia, traveling in Italy, lit candles at Milan's Duomo cathedral in memory of the victims.