A demonstrator is detained by the police during a protest following the grand jury decision in the Ferguson, Missouri, shooting of Michael Brown, in Oakland, California. REUTERS/Stephen Lam

There will be no new grand jury to try Darren Wilson, the police officer who shot dead teenager Michael Brown in Ferguson, Missouri, in August.

A spokesman for state governor Jay Nixon said he would not entertain the idea of bringing in a special prosecutor to present the case to a new grand jury, according to the St Louis Post.

Following Monday's ruling by a grand jury not to charge Wilson for the killing of the 18-year-old, protests and lootings broke out in Ferguson and many other US cities.

Earlier, Nixon had welcomed the "ramped up presence" of the National Guard, tripled from 700 to 2,200 on Tuesday night, in the St Louis suburb.

On Wednesday, 200 protesters gathered outside St Louis City Hall, holding a mock trial of Wilson, reports BBC. Anger spread to 12 other cities, including Philadelphia, New York, Cleveland, Los Angeles and Boston.

Police arrested dozens of demonstrators in downtown Los Angeles after an hour-long protest march.

Wilson has told the US media that he had a "clean conscience" describing how Brown had pushed him back into his car, hit him and grabbed at his drawn gun. Wilson said that he felt "like a five-year-old holding on to [US wrestler] Hulk Hogan".

Brown's mother dismissed his account saying the officer had been "disrespectful" in his comments.