Protest marches have sprung up in cities across the United States, as a huge security operation stifled clashes in Ferguson, the town at the centre of the country's latest racially-charged riots.
Violent unrest erupted in the St Louis suburb for a second night, after Monday's decision by a grand jury not to prosecute a white police officer for shooting dead an unarmed black teenager.
Missouri Governor Jay Nixon said the National Guard force in the Ferguson area had been tripled to more than 2000 troops to back up officers' beleaguered local police force.
A St Louis police patrol car was burnt by protesters on Tuesday and the force declared the demonstration an "illegal gathering," warning marchers and journalists alike that they faced arrest.
Meanwhile, armed Missouri National Guard troopers sealed off West Florissant, the road running through Ferguson that was the scene of the worst looting and arson on Monday night after the verdict was announced.
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At the Ferguson police station riot police dispersed around 100 protesters chanting and waving placards, including one that read: "We will not be silenced."
Meanwhile, thousands of marchers in New York City snaked along streets and freeways, disrupting traffic on bridges and in tunnels - leading to a number of arrests.
A peaceful crowd took to the streets in Washington outside the White House.
Similar angry but largely peaceful protests sprang up in cities large and small, from Oakland and Seattle on the west coast to Atlanta, Philadelphia and Baltimore in the east.
In sprawling Los Angeles, 500 people, a racially-mixed crowd including families and children, marched on police headquarters. In Portland and Denver police reportedly resorted to pepper spray.
CNN reported that gatherings large and small had been reported in 170 communities nationwide.
US President Barack Obama called for rioters to be prosecuted, but acknowledged the deep-rooted frustrations of minorities who feel they are unfairly treated by police.
"There are productive ways of responding and expressing those frustrations and there are destructive ways of responding," he said.
"Burning buildings, torching cars, destroying property, putting people at risk. That's destructive and there's no excuse for it. Those are criminal acts."
Civil rights firebrand Al Sharpton said the Brown case renewed a nationwide fight for greater police accountability.
"This is not a Ferguson problem... This is a problem all over the country," Sharpton said.
Separate protests flared, meanwhile, in Cleveland, Ohio, following the fatal shooting by police of a 12-year-old black boy holding a toy gun at the weekend.
Despite appeals by Brown's family for calm in Ferguson on Monday, protests rapidly degenerated into looting, arson and running street battles between police and stone-throwers.
