FERGUSON, US - National Guard troops were ordered into the US town of Ferguson on Monday after the latest in a week of nightly protests sparked by the police shooting of an unarmed black teenager.

Heavily-armed police in Ferguson, a majority African-American suburb of St. Louis, Missouri launched a crackdown after a white officer gunned down 18-year-old Michael Brown on August 9.

A week later the town is still the scene of nightly clashes and the centre of a renewed national debate about racial divisions and heavy-handed police tactics in suburban America. Missouri Governor Jay Nixon directed the National Guard to “assist ... in restoring peace and order” and put the part-time soldiers under the unified police command in this town of some 21,000 people. President Barack Obama - who last week made brief remarks to appeal for “peace and calm” - was to be briefed on the situation by Attorney General Eric Holder later in the day.

Nixon’s came after police urged tear-gas to disperse the latest protest, which deteriorated into mob violence hours before a midnight curfew imposed for the second night in a row.

Supported by armoured vehicles, police also fired rubber bullets after “Molotov cocktails were thrown,” according to Captain Ron Johnson, the state highway patrol officer charged with restoring order.

“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,” he told reporters. Looters attacked at least four businesses in what Johnson described as “disobedience, preplanned aggression.” Social media posts and pictures from the scene suggested that in one case protesters entered a McDonald’s restaurant to seek milk to rinse teargas from their eyes.

At least two people were wounded by gunfire, Johnson added. “Based on these conditions, I had no alternative but to elevate the level of our response,” said Johnson, who was hailed last week as a moderating force after he replaced local commanders.

Some of the demonstrators carried signs protesting police brutality. Many 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 centre to kneel in protest in front of the police, to say ‘our hands are up’,” said Lisha Williams.

Meanwhile, the local school district said classes would be cancelled on Monday “due to continuing unrest in some areas ... and in the interest of the safety of students and families.”

Brown was shot at least six times - twice in the head - according to Michael Baden, a former New York City chief medical examiner who conducted a private autopsy at the family’s request. “This information could have been released on day one,” Baden told The New York Times.

Daryl Parks, a Brown family attorney, said the results were released for reasons of transparency. “It shows you that Michael was hit several times by the bullets from the officer,” he told CNN.

The Brown family planned to hold a news conference later Monday. Brown’s relatives have accused police of smearing their son’s character they said he was suspected of robbing a convenience store and released a surveillance video of the incident.

Police said the officer who shot Brown was unaware of the robbery, and stopped the teen for walking in the middle of the street. The US Justice Department, meanwhile, said a federal medical examiner would also carry out an autopsy on Brown’s body, citing the case’s “extraordinary circumstances.”