Missouri's governor on Monday ordered National Guard troops to help restore order in Ferguson, hours after police hurled tear gas to disperse violent protesters in the town wracked by race riots.
Ferguson has endured days of violence since a white police officer on August 9 shot dead Michael Brown, an unarmed black 18-year-old.
The National Guard soldiers will respond to the unified police command in Ferguson, Governor Jay Nixon said in an executive order.
Late Sunday, after a day of peaceful marches, police in body armor and gas masks moved in with armored vehicles to disperse a mob about three hours before the midnight Sunday (0500 GMT Monday) curfew.
Police responded with tear gas after "Molotov cocktails were thrown," said Ronald Johnson, the African-American state highway patrol captain charged with restoring local order, speaking at a press conference after the violence subsided.
"There were shootings, looting, vandalism and other acts of violence that clearly appear not to have been spontaneous but premeditated criminal acts designed to damage property, hurt people, and provoke a response," Johnson said.
Looters attacked at least four businesses, including a McDonald's restaurant and a Domino's Pizza.
Johnson described the violence as "disobedience, preplanned aggression."
At least two people were wounded by gunfire among the protesters, Johnson said. He did not say how many people had been arrested.
Just before 9:00 pm, hundreds of protesters marched toward the police command post, and people in the crowd threw "multiple" Molotov cocktails, bottles and rockets at police.
"Based on these conditions, I had no alternative but to elevate the level of our response," Johnson said.
Some of the marchers carried signs protesting police brutality. Many in the crowd marched peacefully with their hands up in the air, but others taunted police and threw back tear gas canisters.
"We were walking up peacefully towards the command center to kneel in protest in front of the police, to say 'our hands are up,'" said Lisha Williams, who was in the march.
"They started firing tear gas at us out of the blue. I know what tear gas is, my face was burning," said Williams, who described herself as an army veteran.
Governor Nixon said in a statement that he was directing the National Guard to "assist" police "in restoring peace and order to this community."
Brown was shot at least six times -- twice in the head and four times in the right arm -- the New York Times reported, citing a preliminary private autopsy.
All the shots were fired into his front, the Times reported, citing Michael Baden, the former New York City chief medical examiner who conducted an autopsy at the family's request.
"This information could have been released on Day One," Baden told The Times.
Baden, 80, is a high-profile forensic pathologist who has testified at the trial of OJ Simpson, and was consulted for investigations into the deaths of John F. Kennedy and actor John Belushi.
Benjamin Crump, the attorney representing Brown's family, said on Twitter that he and Baden would hold a press conference Monday morning.
Crump, who has called Brown's death an "execution," earlier represented the family of Trayvon Martin, the unarmed black 16-year-old shot dead in Florida in 2012.
Brown's family has accused authorities of a "devious" attempt to smear their son's character after police named him as a suspect in a convenience store robbery and released a surveillance video of the incident.
Police said the officer who shot Brown, unaware of the robbery, stopped the teen for walking in the middle of the street.
The late Sunday protest followed a much larger and peaceful event at the Greater Grace Church in Ferguson honoring Brown.
Captain Johnson, who grew up in the St Louis area, apologized for the shooting.
"I want to start off by talking to Mike Brown's family. I want you to know my heart goes out to you, and I say that I'm sorry," Johnson said to loud cheering and applause from a crowd of more than 1,000. Hundreds more stood outside.
Young people gathered outside the church held their hands in the air, paying homage to what some witnesses said was Brown's last gesture before being shot.
Civil rights activist Jesse Jackson, who was at the morning event, was surprised later about the evening violence.
"I'm astonished at the reversal of the mood," he told CNN.
Amid the growing violence, the federal government has stepped up its involvement in the investigation.
Attorney General Eric Holder will brief President Barack Obama on the Ferguson violence on Monday, the White House said.
"Our immediate goal is to make sure that the residents of Ferguson are safe, that the looting stops, that the vandalism stops, that the people who are living in the community are confident that justice will be done," Obama senior advisor Valerie Jarrett told AURN radio.
FBI agents are already in Ferguson interviewing witnesses to the shooting, officials said.
The US Justice Department also said that a federal medical examiner would carry out an autopsy on Brown's body, citing the case's "extraordinary circumstances."