Slain US teenager Michael Brown's mother says it has been a "sleepless, very hard, heartbreaking and unbelievable'' time for her since the grand jury's decision not to indict Ferguson police officer Darren Wilson for killing her son.

Lesley McSpadden said on Wednesday during an interview on NBC's "Today" show that she felt that Wilson's description of her son as looking demonic during their August 9 confrontation was disrespectful and "added insult to injury".

"I don't believe a word of it. I know my son far too well to... he would never do anything like that. He would never provoke anyone to do anything to him and he wouldn't do anything to anybody...,"

Michael Brown's mum,

The family spoke out after officer Wilson said in his first televised interview since the incident that Brown resembled an angry "demon" who had started the confrontation, grabbing for his gun and later rushing toward him.

"I don't believe a word of it. I know my son far too well to... he would never do anything like that. He would never provoke anyone to do anything to him and he wouldn't do anything to anybody...," McSpadden said in a separate interview on CBS television.

His father, Michael Brown Sr, said on NBC he felt the officer's version of events was "crazy."

"For one, my son, he respected law enforcement," Brown said. "Two, who in their right mind would rush or charge at a police officer that has his gun drawn? It sounds crazy."

The parents' attorney also rejected Wilson's description of Brown.

"When you have people of colour be killed they try to demonise and play on the stereotypes, and they try to put the police officer who killed our children on a pedestal," Benjamin Crump told NBC. "It's just not right, and we have to fix this system."

Civil rights activists are demanding greater accountability and transparency in the police force.

Reverend Al Sharpton, who met with the Brown's famiily, said this latest death should lead to a new era in the police force.

"Not only do they share the pain of being victims of police conduct. But this will be their first thanksgiving with an empty seat at the table," Al Sharpton said.

"This is the first year suffered a loss, and i hope that america will understand tha whatever your opiion. These are real human beings and the value of their sons and husbands shouldn't be minismed by anybody," he added.

Nationwide rallies

Protests have flared across the United States after Monday's decision by a grand jury not to prosecute the white police officer for shooting dead the unarmed black teenager.

One of the protest marches on Wednesday included about 200 people who began with a mock trial of Darren Wilson. Later an undetermined number of protesters made it into the City Hall in St Louis shouting "Shame, shame".

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More than 100 additional police officers were called to the building and it was locked down.

A total of 58 people were arrested at area protests overnight, including 45 in Ferguson.

Country music star Garth Brooks has cancelled scheduled appearances this week, saying it would be in poor taste to promote his comeback album in the midst of the national protests.

"To spend the day promoting our stuff like nothing was wrong, seemed distasteful to me," Brooks said in a Facebook post on Tuesday.

Earlier on Tuesday, Missouri governor, Jay Nixon, ordered more than 2,200 National Guardsmen troops to the region near Ferguson rocked by rioting.

Source: Agencies