For the fourth straight night Thursday tear gas filled the air in Ferguson, Missouri, where hundreds of protesters again clashed with police.
Tensions continue to boil over after the death of 18-year-old Michael Brown, the unarmed teenager shot and killed after a confrontation with police last weekend.
The build up of officers, many in tactical and riot gear, started before the sun went down.
Earlier many of those marching for justice also called for calm.
Brown's parents have condemned the violence in the wake of their son's death, along with local pastors, public officials and police.
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