More than 1,000 protesters shouted slogans at riot police in St. Louis in the early hours of Monday near the climax of four days of street rallies and sit-ins over the police shootings of two black 18-year-olds.
Many on the night march chanted, "Indict, convict, put the killer cops in jail. The whole damn system is guilty as hell," in the city where a white off-duty officer shot and killed teenager Vonderrit Myers Jr. last week. Police said the youth had opened fire.
Almost two months to the day earlier, another white officer shot and killed unarmed teenager Michael Brown in the St Louis suburb of Ferguson after what police described as an altercation.
The shootings have focused global attention on the state of race relations in the United States and evoked memories of other racially-charged cases, including the fatal shooting of black 17-year-old Trayvon Martin in Florida in 2012.
Officers in riot gear beat their batons on the ground in unison as they faced off against the marchers, before letting them walk peacefully on.
"You make my heart easier," Myers' father told the crowd that later gathered in the St Louis University campus and held a four-minute silence.
Hundreds of activists have traveled from across the United States to join four days of protests, dubbed "Ferguson October." Organizers said the event would culminate in mass rallies later on "Moral Monday."
Police arrested seventeen protesters staging a sit-in at the entrance to a convenience store early on Sunday in the Shaw neighborhood where Myers was killed.
Brown's death triggered a national uproar in August over police accountability and protesters have called for the arrest and prosecution of the officer, Darren Wilson. A grand jury is considering the case.
Protest leaders said they were also planning acts of civil disobedience on Monday, without going into detail.
"I came here to go to jail," activist, author and academic Cornel West told hundreds of people who turned out at an arena in St. Louis on Sunday evening.
(This version of the story corrects wording of chant in second paragraph, and fixes location of speech in sixth paragraph)
(Reporting by Fiona Ortiz and Kenny Bahr; Editing by Chris Michaud and Andrew Heavens)