National Guard sent in

Photo: The Canadian Press. All rights reserved.

Police wait to advance after tear gas was used to disperse a crowd Sunday, Aug. 17, 2014, during a protest for Michael Brown, who was killed by a police officer last Saturday in Ferguson, Mo. (AP Photo/Charlie Riedel)

Missouri's governor on Monday ordered the National Guard to a St. Louis suburb convulsed by protests over the fatal shooting of an unarmed black teen, after a night in which police used tear gas to clear protesters off the streets well ahead of a curfew.

Gov. Jay Nixon said the National Guard would help restore 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.

The latest confrontations in Ferguson came on the same day that U.S. Attorney General Eric Holder ordered a federal medical examiner to perform another autopsy on Brown, and as a preliminary private autopsy reported by The New York Times found that Brown was shot at least six times, including twice in the head.

Brown's death heightened racial tensions between the predominantly black community and the mostly white Ferguson Police Department. Civil rights activists have compared the shooting to other racially charged cases, especially the 2012 death of Trayvon Martin, the unarmed black teenager shot by Florida neighbourhood watch organizer who was later acquitted of murder. Both cases have fueled nationwide debates on the treatment of young black men in America.

As night fell in Ferguson Sunday, another peaceful protest quickly deteriorated and the streets were empty well before the midnight curfew.

Capt. Ron Johnson of the Missouri Highway Patrol, who is command in Ferguson, said at least two people were wounded in shootings by civilians, he said.

"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.

The "extraordinary circumstances" surrounding Brown's death and a request by his family prompted the Justice Department's decision to conduct a third autopsy, agency spokesman Brian Fallon said in a statement. The examination was to take place as soon as possible, Fallon 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.

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 neighbourhood where Brown was shot to death Aug. 9.

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.

Brown was also shot four times in the right arm, and all the bullets were fired into his front, Baden said.

Police have said little about the encounter between Brown and the officer, except to say that it involved a scuffle in which the officer was injured and Brown was shot. Witnesses say the teenager had his hands in the air as the officer fired multiple rounds.

The officer who shot Brown has been identified as Darren Wilson, a six-year police veteran who had no previous complaints against him. Wilson has been on paid administrative leave since the shooting. Associated Press reporters have been unable to contact him at any addresses or phone numbers listed under that name in the St. Louis area.