Street protests in the predominantly African-American community of 21,000 people have been punctuated by looting, vandalism and clashes between demonstrators and police every night since 18-year-old Michael Brown was killed by a white police officer.

A grand jury was expected to begin a criminal inquiry into shooting on Wednesday.

Earlier Tuesday, St. Louis metropolitan police said they shot and killed a 23-year-old black man who brandished a knife at officers and yelled at them to "shoot me now, kill me."

Two officers opened fire after he refused repeated orders to drop his weapon, police said. The incident occurred a few miles from the scene of the protests.

While apparently unrelated to the Brown killing or protests surrounding it, the shooting sparked concerns about an escalation of public anger over what many perceive as a pattern of excessive police force against minorities.

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