FERGUSON, United States - Protest marches sprang up in cities across the United States on Tuesday, amid a tense security operation in Ferguson, the Missouri town at the centre of the country's latest racially-charged stand-off.
Clashes 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 be tripled to more than 2,000 troops to back up the officer's beleaguered local police force.
Armed National Guard troopers sealed off West Florissant, the road running through Ferguson that was the scene of the worst looting and fire-starting on Monday. Police made at least two arrests.
St Louis police said that one of their patrol cars had been vandalized by protesters who were trying to set it on fire.
At the Ferguson police station a cordon of 50 riot police faced off across a road with around 100 noisy protesters chanting and waving placards, including one that read: "We will not be silenced." Inside the perimeter of the station, National Guardsmen equipped with riot shields and batons could be seen preparing for the night.
The protest crowd was smaller than it had been on Monday, but some masked agitators could be seen on the fringes of the demonstration and the mood was tense.
"Lives and property must be protected. This community deserves to have peace," Governor Nixon said, as anger mounted nationwide.
Meanwhile, marchers disrupted traffic on bridges and in tunnels in New York city - leading to a number of arrests - and a peaceful crowd took to the streets in downtown Washington, near the White House.
Similar angry but largely peaceful protests sprang up in cities large and small, from Los Angeles and Seattle on the west coast to Atlanta, Philadelphia and Baltimore in the east.
US President Barack Obama called for rioters to be prosecuted, while acknowledging 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."
Lawyers for the family of slain youth Michael Brown denounced the prosecutor whose grand jury hearing found that police officer Darren Wilson had killed the 18-year-old in self-defence.