Calls for calm after US police kill teen

Washington - A southern US mayor called for calm on Monday after the weekend police shooting of an unarmed black teenager ignited a night of violence that left two officers injured and 32 people arrested.

Mayor James Knowles of Ferguson, a suburb of St Louis, Missouri promised a thorough and impartial investigation by county officials into Saturday's death of aspiring college student Michael Brown, 18.

"The only thing I can tell my community now is to remain calm," said Knowles on CNN television. "I understand the rage and anger of people, but this is not constructive."

St Louis County police said two officers were injured overnight and 32 people arrested for theft, assault or burglary. Local schools cancelled what would have been their first day back after summer.

Footage posted by the St Louis Post-Dispatch newspaper showed a gas station store in Ferguson - a town of 21 000 residents, two-thirds of them African-American - plundered and set on fire.

Looters also raided a Walmart and several other smaller stores, and set fires elsewhere, it reported.

Gathered for vigil

The violence broke out after large crowds of mostly African-American protesters gathered on Sunday for a vigil at the spot where Brown was fatally shot by a Ferguson police officer.

Knowles told CNN his administration would take "a hands-off approach" to what he pledged would be an "impartial" investigation by St  Louis County authorities.

"We want people to have faith in the process... As a [city] government, we're not going to be involved in this investigation because we want people to be confident in the process."

Details of Brown's death differed. A witness identified as Dorian Johnson told KMOV News 4 that he was walking with Brown when a police officer confronted them and drew his weapon.

The officer shot Brown, who "turned around and put his hands in the air", Johnson said. "He started to get down and the officer still approached with his weapon drawn and fired several more shots."

But St Louis County Police Chief Jon Belmar told a news conference on Sunday that Brown was killed after physically assaulting a police officer and struggling to get his weapon.

Belmar did not say whether the officer was white.

Tension between police, community

The Post-Dispatch said the incident brought to light a lingering tension between the mostly white local police force and the suburb's African-American majority.

"The death of yet another African-American at the hands of those sworn to protect and serve the community where he lived is heartbreaking," said Cornell Williams Brooks of the NAACP, the Post-Dispatch reported.

"Michael Brown was preparing to begin college, and now his family is preparing to bury their child - his life cut short in a tragic encounter with the police," he added.

Brown's grief-stricken mother, Lesley McSpadden, told KMOV TV her son had just graduated from high school.

"Do you know how hard it was for me to get him to stay in school and graduate? You know how many black men graduate? Not many," she said.

"Because you bring them down to this type of level, where they feel like they don't got nothing to live for anyway."

Benjamin Crump - the lawyer who represented the family of Trayvon Martin, the black teen shot and killed in Florida by George Zimmerman, a neighbourhood watchman, in February 2012 - said on Twitter he has been hired by Brown's family to represent them.

Zimmerman, who pleaded self defence, was acquitted the following year of second-degree murder and manslaughter - sparking anger among those who thought his actions had been racially motivated.