Chicago (AFP) - Thousands of hate crimes are reported in the United States every year, but rarely do they involve the carnage seen at a black church in South Carolina where nine people were gunned down during a Bible study meeting.
Wednesday's attack provoked comparisons to the 1963 bombing of a Birmingham church, which killed four little girls and wounded more than 20 congregants in one of the deadliest attacks carried out during the civil rights movement.
"The fact that this took place in a black church obviously also raises questions about a dark part of our history," President Barack Obama said Thursday.
"This is not the first time that black churches have been attacked. And we know that hatred across races and faiths pose a particular threat to our democracy and our ideals."
The attack was also reminiscent of the 2012 attack on a Sikh temple by a white supremacist US military veteran that left six people dead in Wisconsin.
The death toll in Charleston is "unprecedented" in terms of recent US incidents of racially-motivated violence, said Jens David Ohlin, a law professor at Cornell University.
Most of the mass shootings that have stunned the nation in recent years were perpetrated by mentally disturbed people with no political motive.
But the accused Charleston gunman -- 21-year-old Dylann Roof -- is believed to be a white supremacist who reportedly told his victims: "I have to do it. You're raping our women and taking over the country. You have to go."
- Are hate crimes 'terrorism'? -
The shooting comes at a time of heightened racial tensions in America, with many questions raised about police tactics, especially with respect to minorities, after several high-profile deaths of black men at the hands of white officers.
The Charleston carnage immediately provoked calls to label the attack as terrorism, in part to recognize the nation's long history of racial violence.
"Radicalism can come in many different forms. One can be a Muslim supporter of IS, and another a far-right racist," said Max Abrams, a political science professor at Northeastern University in Boston.
"We need to apply a consistent set of standards in terms of labeling incidents as terrorism or not," he told AFP. "It's unfair otherwise because people might be left with the impression that only Muslims commit terrorist attacks."
Richard Cohen, president of the Southern Poverty Law Center, agreed.
"Since 9/11, our country has been fixated on the threat of jihadi terrorism. But the horrific tragedy at the Emanuel AME reminds us that the threat of homegrown domestic terrorism is very real," Cohen said.
The United States utterly reshaped its security apparatus and invested billions in trying to protect itself from terrorists in the wake of the attacks of September 11, 2001.
While the focus has been on capturing jihadists, non-jihadist extremists have proven to be more deadly in recent years, according to an analysis by the New America Foundation.
A total of 26 people were killed in seven attacks by jihadists on US soil in the 14 years since Al-Qaeda militants killed more than 3,000 people in New York, Washington and Pennsylvania after hijacking four airplanes.
The deadliest of those attacks was the 2009 shooting by army psychiatrist Nidal Hasan, who killed 13 people and wounded more than 30 others at Fort Hood in Texas.
During the same period, the New America Foundation tracked 18 attacks by right-wing extremists that left 39 people dead.
The list included the slaying of three people by a neo-Nazi at a Kansas Jewish center last year and the Sikh temple attack in 2012.
Nearly half of the nearly 6,000 hate crimes tracked by the Federal Bureau of Investigation in 2013 were racially motivated. Two-thirds of those attacks were motivated by a bias against blacks.
There are currently 784 hate groups operating in the United States, according to the Southern Poverty Law Center.
While the number has dropped off significantly after skyrocketing in the wake of Obama's election in 2008, it remains 30 percent higher than it was in 2000.
The growth was fueled by "anger and fear over the nation's ailing economy, an influx of non-white immigrants, and the diminishing white majority, as symbolized by the election of the nation's first African-American president," the civil rights group said in its latest report.