Violent protests erupts in Ferguson

President Barack Obama and the family of slain 18-year-old Michael Brown separately appealed for calm after the St Louis prosecutor revealed the jury's verdict.

But members of an angry crowd outside the police station where Officer Darren Wilson had been based began throwing bottles and stones. Riot officers responded with teargas.

As St Louis County Prosecuting Attorney Robert McCulloch rounded up his summary of the decision, Brown's mother burst into tears and the crowd began to chant: "Hey, hey, ho, ho! These killer cops have got to go."

In Washington, Obama made a rapidly-organized televised appearance to appeal for calm in the Midwestern town, echoing the sentiments of the dead teenager's family.

"Michael Brown's parents have lost more than anyone. We should be honoring their wishes," Obama said.

"I also appeal to the law enforcement officials in Ferguson and the region to show care and restraint in managing peaceful protests that may occur."

His words fell on deaf ears in Ferguson, where police were pelted with bricks and bottles and responded with volleys of teargas.

McCulloch told reporters the evidence presented to the grand jury had suggested Wilson had shot as a legitimate act of self-defense during a tussle that broke out as he was responding to a robbery.

He said "an altercation" had broken out as Wilson was sitting in his patrol car and Brown was standing at the window.

"During the altercation, two shots were fired by Officer Wilson while still inside the vehicle," McCulloch said.

After these shots were fired, Wilson is said to have left the car to pursue Brown, who turned on him. More shots were fired and the young man was killed.

McCulloch said forensic evidence showed that Wilson -- who was himself slightly hurt in the tussle -- had shot twice from within his car and 10 more times as he confronted Brown in the street.

In August, some early witnesses had said that Brown had his hands up and was surrendering when he was killed. But McCulloch said the physical evidence and other witnesses contradicted this account.

"Decisions on a matter as serious as charging an individual with a crime simply cannot be decided on anything less than a complete critical examination of all available evidence," he said.

In a statement, the Brown family said: "We are profoundly disappointed that the killer of our child will not face the consequence of his actions.

"We respectfully ask that you please keep your protests peaceful," the family added, calling for legal reform. "Answering violence with violence is not the appropriate reaction."

The shooting of Brown, an 18-year-old who had planned to go to college, sparked weeks of sometimes violent protests and a nationwide debate about police tactics and race relations.

Before the verdict, St Louis Mayor Francis Slay admitted that "what happened to Michael Brown has deeply divided us."

Ferguson's mainly African American community of 21,000 has been on edge for days, braced for further protests should the officer not be indicted.

The mostly black suburb has an overwhelmingly white police force and residents complain of years of racial prejudice and heavy handed police tactics.

In the days leading up to the decision, Missouri's governor declared a state of emergency and called up the National Guard last week in readiness. The FBI has also deployed extra personnel.

Shops were boarded up in Ferguson and schools in the Ferguson-Florissant District announced they would be closed Tuesday for the safety of staff and pupils.