Gov Jay Nixon said the National Guard would help "in restoring peace and order" to Ferguson, where protests over the killing of 18-year-old Michael Brown by a white police officer entered their second week.
Police said they acted in response to gunfire, looting, vandalism and protesters who hurled Molotov cocktails.
"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 in a statement.
As night fell in Ferguson yesterday, another peaceful protest quickly deteriorated and the streets were empty well before the midnight curfew.
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"Based on the conditions, I had no alternative but to elevate the level of response," said Capt. Ron Johnson of the Missouri Highway Patrol, who is command in Ferguson. At least two people were wounded in shootings, he said.
The results of a state-performed autopsy would be taken into account along with the federal examination in the Justice Department investigation, Fallon said.
Dr Michael Baden, a former New York City chief medical examiner, told The New York Times that one of the bullets entered the top of Brown's skull, suggesting that his head was bent forward when he suffered a fatal injury.
The Justice Department already had deepened its civil rights investigation into the shooting. A day earlier, officials said 40 FBI agents were going door-to-door gathering information in the Ferguson neighborhood where Brown was shot to death August 9.