The National Guard has been sent to the town of Ferguson as protests escalate over the police shooting of black teenager Michael Brown.
Missouri Governor Jay Nixon signed an order to “help restore peace and order and to protect the citizens of Ferguson”.
The decision was made as police clashed with angry crowds shortly before a second night under curfew began.
Police in Ferguson, a suburb of St Louis, said they came under attack and had “no alternative” but to respond.
Captain Ron Johnson said protesters had thrown Molotov cocktails and bottles at security forces, and set up barricades before the five-hour curfew began at midnight on Sunday.
“For those who would claim that the curfew was what led to [the] violence, I will remind you this incident began three and a half hours before the curfew was to have started,” Ron Johnson told journalists in Ferguson on Monday.
Correspondents at the scene described seeing smoke clouds rise up as police began to disperse the protests on West Florissant Avenue, with a helicopter beaming down a spotlight.
Some of the demonstrators were spluttering and poured bottles of water into their eyes as they felt the effects of tear gas. Others sought cover from the unrest inside a fast food restaurant.
The killing of Michael Brown by a white policeman in a street on August 9 has inflamed racial tensions in the largely black suburb.
Officer Darren Wilson shot Michael Brown after reportedly stopping him for walking in the street, disrupting traffic.
Governor Jay Nixon has criticized police for releasing surveillance video which apparently shows Michael Brown stealing some hours before his death.
Jay Nixon said the release of the footage “appeared to cast aspersions” on the dead man, saying “it made emotions raw”.
He also condemned the protesters: “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.”
A preliminary post-mortem examination by the St Louis County Medical Examiner’s office on the day after Michael Brown’s death found he had been shot, police said, without disclosing how many times.
However, a preliminary private post-mortem report has since revealed that he was shot at least six times, including twice in the head, the New York Times reports.
The bullets did not appear to have been fired from very close range due to the lack of gunpowder on the victim’s body, forensic pathologist Michael Baden was quoted by the paper as saying.
Michael Baden flew to Missouri on Sunday to conduct a separate autopsy at the request of the family.
Officials last week confirmed that Darren Wilson was a six-year police veteran with no previous complaints against him. He has been on paid administrative leave since the shooting.
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