Every night this week, on the grim streets of Ferguson, Mo., a mostly black St. Louis suburb, heavily armed police have resorted to stun grenades and tear gas in violent confrontation with angry protesters after Michael Brown, an unarmed 18-year-old African-American was shot and killed by a white officer last weekend.
Barack Obama briefly broke his golf-and-beach vacation Thursday on the elite island playground of Martha's Vineyard to decry the violence, only the third time in his presidency that he has publicly waded into specific street crimes, all of them involving African-American victims.
"There is never an excuse for violence against police or for those who would use this tragedy as a cover for vandalism and looting," Mr. Obama said. "There's also no excuse for police to use excessive force against peaceful protests or to throw protesters in jail for lawfully exercising their First Amendment rights."
As outrage grew over the tough tactics used by local police, Missouri Governor Jay Nixon put state police in charge on Thursday.
"What's gone on here over the last few days is not what Missouri is about; it is not what Ferguson is about," the Governor said, adding that Missouri Highway Patrol Captain Ron Johnson, an African-American who grew up in the Ferguson area, would oversee the security effort.
Across the United States, leaders sought to defuse the new outbreak of racially charged violence before it spills beyond the bleak confines of Ferguson.
Inside a packed church in north St. Louis on Thursday, Senator Claire McCaskill, a Missouri Democrat, got a standing ovation when she called for police to "demilitarize" their approach. SWAT teams, riot squads and even armoured vehicles with helmeted policeman clad in body armour manning machine guns in turrets have confronted crowds of protesters.
Disturbing images have emerged from Ferguson: billowing clouds from tear-gas canisters and smoke bombs; squads of white police pointing assault rifles at black protesters. "This kind of response by the police has become the problem instead of the solution," Ms. McCaskill said.
But even as the President and others appealed for calm, others stoked the fires of racial division.
Benjamin Crump, the lawyer representing Mr. Brown's family, has fuelled African-American anger, saying the killing was worse even than the shooting of a 17-year-old unarmed African-American by a neighbourhood watchman in Florida two years ago. "Trayvon Martin was shot by a single shot by an untrained civilian. Michael Brown was executed by a trained police officer."
Ferguson Police Chief Thomas Jackson has refused to identify the officer who fatally shot Mr. Brown last weekend, claiming that naming him could endanger the policeman and his family. Chief Jackson heads a 53-officer force – only three of whom are African-American; 70 per cent of residents in Ferguson are black.
Police have defended their tactics, claiming the protests following Mr. Brown's death have repeatedly turned violent.
St. Louis County Police Chief Jon Belmar claimed his force has responded with "an incredible amount of restraint" amid a hail of rocks and bottles thrown as well as occasional gunfire. He said more than 20 police vehicles have been destroyed.
"It's scary," said Brian Schellman, a police spokesman, adding officers "hear gunshots going off, and they don't know where they're coming from."
Mr. Obama has ordered independent probes by both the Federal Bureau of Investigation and the Justice Department.
"It's important to remember how this started," the President said. "We lost a young man, Michael Brown, in heartbreaking and tragic circumstances. His family will never hold Michael in their arms again. And when something like this happens, the local authorities – including the police – have a responsibility to be open and transparent."
So far, two mostly irreconcilable versions of the shooting have emerged. Police claim the fatal shots were fired after several men forcibly resisted an officer's attempt to arrest them and the policeman suffered facial lacerations and bruising.
Several witnesses to the daylight shooting claim Mr. Brown had his hands up and was surrendering when he was gunned down by an officer who shot him multiple times.
Since Sunday, protesters have confronted police holding their hands in the air and chanting, "Hands up, don't shoot." But there have also been outbreaks of looting, vandalism and violence.
"Even if we disagree, this climate is not good for anyone and is dangerous for everyone," civil-rights activist Al Sharpton said in a statement.
Internet hacking activists in the group that calls itself Anonymous posted a name of the officer they claimed was responsible for the shooting and threatened to add details including his photograph, but both the Ferguson and St. Louis police departments denied having any officer with that name in their ranks.
The case is already in the courts. The American Civil Liberties Union filed suit Thursday to get the police incident report under Missouri's Sunshine Law after police refused to release it.
"What is now urgently needed are thorough investigations, not further inflammation, of the incredibly tense situation in the aftermath of Michael Brown being shot dead," said Erika Guevara Rosas, Americas Director at Amnesty International.
Meanwhile, two reporters were handcuffed and arrested by police who refused to identify themselves on Wednesday night. "We are concerned by the detention and harassment of reporters trying to cover the news in Ferguson," said Robert Mahoney, deputy director of the Committee to Protect Journalists.
Mr. Obama has twice previously voiced his views on high-profile, racially charged cases. In 2012, after Mr. Martin was killed in Florida, the President said: "If I had a son, he would look like Trayvon."
And in 2009, when Henry Louis Gates, a black Harvard professor, was arrested on his own front doorstep, Mr. Obama said: "The Cambridge police acted stupidly in arresting somebody when there was already proof that they were in their own home."
The President has said he too has lived the experience of police and whites treating African-Americans as though they are either dangerous or criminals.
According to polls, African-Americans are much more likely than whites to say they are subjected to unfair treatment in dealing with police or in the courts. In a Pew Research Center survey conducted last year, seven in 10 blacks said that blacks in their community were treated less fairly than whites in dealings with the police. In comparison, 37 per cent of whites and 51 per cent of Hispanics held that view.