Four police officers in Minneapolis, Minnesota, were fired following Monday's arrest of an African American man who died after one white officer knelt on his neck.
A bystander captured the scene on video and posted it on social media, and it was quickly broadcast across the country.
Minneapolis Mayor Jacob Frey tweeted Tuesday that relieving the four officers of their jobs is "the right call."
"He should not have died. What we saw was horrible. Completely and utterly messed up. This man's life matters," the mayor said. "I believe what I saw and what I saw was wrong at every level. Being black in America should not be a death sentence."
Minneapolis police say the victim, George Floyd, resembled a suspect wanted in a forgery case, and that officers acted after Floyd resisted arrest.
The video shows a white officer holding a handcuffed Floyd on the ground and kneeling on his neck.
"Please, please, please, I can't breathe. Please, man," Floyd can be heard saying, while bystanders yell at police to ease up on him.
The officer on top of Floyd urges him to "relax," but keeps his knee on Floyd's neck for several minutes after the victim stopped moving. One witness said he heard Floyd calling out for his mother before dying.
Minneapolis police are promising a full investigation, while the FBI will look into whether Floyd's civil rights were violated.
Hundreds of people gathered Tuesday evening at the spot where Floyd died to protest the tragedy. They marched a few kilometers to a police precinct, where they clashed with police in riot gear. Protesters vandalized at least one police squad car, broke the windows of the precinct building and sprayed the graffiti on the front of the building. Police responded by firing tear gas and non-lethal projectiles at the demonstrators.
Kneeling on a suspect's neck is an acceptable tactic for a suspect resisting arrest in Minneapolis and the city's police union is asking the public to wait until the investigation is complete before "rushing to judgment and immediately condemning our officers."
Monday's death drew comparisons to Eric Garner, an unarmed black man in New York who died in 2014 after a white officer placed him in a chokehold while he begged for his life. Garner also pleaded with officers that he could not breathe.
Floyd's death also comes weeks after three people were charged with February's fatal shooting in Georgia of Ahmaud Arbery. He was allegedly killed by a white former Glynn County police officer and his son who apparently mistook Arbery for a burglar while he was jogging. They were charged after a video of the shooting emerged. The man who shot the video was also charged.
In what became a rallying cry for the Black Lives Matter movement, a white police officer shot an unarmed black man in the back as he was running away on foot after a traffic stop in 2015.
As officer Michael Slager appeared in a South Carolina court before receiving a 20-year sentence for killing Walter Scott, Scott's mother turned to Slager and told him "I forgive you." Slager responded to Scott's mother, Judy, by mouthing the words "I'm sorry" as she sat nearby.
The U.S. has a long history of deadly violence by police against blacks and other minorities.
"About 1 in every 1,000 black men can expect to be killed by police," according to a study by the journal Proceedings of the National Academy of Sciences of the United States of America.
The study found that "Black women and men and American Indian and Alaska Native women and men are significantly more likely than white women and men to be killed by police. Latino men also are more likely to be killed by police than are white men."