"These violent acts are a disservice to the family of Michael Brown and his memory and to the people of this community who yearn for justice to be served and to feel safe in their own homes," Nixon said.
Authorities said they were responding to reports on Sunday of gunfire, looting, vandalism and protesters hurling Molotov cocktails. The local school district canceled classes, scheduled for Monday, out of concern for the safety of children amid the violence.
The clashes have caught international attention, with U.N. Secretary-General Ban Ki-moon issuing a statement Monday urging law enforcement organizations to respect protesters' rights.
"The Secretary-General calls on the authorities to ensure that the rights to peaceful assembly and freedom of expression are protected," U.N. spokesman Stephane Dujarric told reporters.
The National Guard call-up represents authorities’ second attempt to quell protests that started last week after Brown’s death on Aug. 9. The first such attempt came last Thursday, when the governor placed local Ferguson City and St. Louis County police in the city under the command of the state’s highway patrol — after city forces responded to protests with SWAT teams and sniper rifles pointed in the direction of unarmed demonstrators.
That switch brought a day of what seemed like reconciliation between citizens and police. But Friday – after Ferguson city authorities released a video allegedly showing Brown taking a pack of mini-cigars from a convenience store shortly before his shooting – clashes resumed.
Many saw the release of the video as an unfair attack against Brown, noting that police acknowledged that the officer who shot him did not know he was a suspect in the theft. Police say Wilson stopped Brown at first for walking in the middle of the street. Brown’s family and supporters have described the robbery allegations as character assassination.
The governor’s decision and the latest confrontations between police and protesters came just hours after Attorney General Eric Holder ordered a federal medical examiner to perform a third autopsy on Brown. On Sunday, the results of a preliminary autopsy of the victim showed he had been shot six times — four times in the right arm and two times in the head. A private examiner performed that autopsy on the Brown family’s behalf.
Another expert, Shawn Parcells, a pathologist hired by the family, said Monday that one a bullet wound to his arm may have happened when he put his hands up, "but we don't know."
At a news conference with Brown family and its legal team, Parcells said that a graze wound on Brown's right arm could have occurred in several ways. He says the teen could have had his back to the shooter, or he could have been facing the shooter with his hands above his head or in a defensive position.
Brown’s mother Lesley McSpadden spoke on ABC’s “Good Morning America” talk show Monday and said that justice would be for Wilson to face arrest and prosecution in the death of her son.
She added that Capt. Ron Johnson, the highway patrol officer responsible for overseeing the response to the unrest, met with them Sunday and apologized for the death of their son. Capt. Johnson, who is black, also told the parents that Brown could have been his son, McSpadden said.
Meanwhile, confusion reigned in Ferguson, with demonstrations becoming violent after an earlier period of calm.
A crowd of about 400 appeared peacefully marched Sunday, but a spokesman for the Missouri Highway Patrol said that "aggressors" were trying to infiltrate a law enforcement command post, and that armored vehicles were deployed to ensure public safety.
"We ordered them back. We ordered them back again. After several attempts, we utilized the smoke to disperse these individuals," said Justin Wheetley of the highway patrol.
"The smoke bombs were completely unprovoked," said Anthony Ellis, 45. "It [the protest] was led by kids on bikes. Next you know, they're saying, 'Go home, Go home!'"
With tensions high Sunday night, several journalists said they faced threats of violence from police.
One journalist broadcasting a livestream of events on the Internet reported an officer threatening to shoot him if he did not obey his commands to turn off his camera light and leave. Several others reported being briefly detained by police.
MSNBC reporter Chris Hayes, tweeting Sunday night, said an officer gave him an unequivocal warning.
Hayes tweeted, “Riot cop to me just a few minutes ago: ‘Get back! Or next time you're gonna be the one maced.'"
Al Jazeera and wire services. Ryan Schuessler contributed to this report