Rumain Brisbon
Rumain Brisbon, 34, was shot dead in Phoenix, Arizona Facebook

An unarmed black man was killed by a white police officer who mistook a pill vial for a gun, in an incident that has fuelled more social unrest in the US, over the police's perceived excessive use of force against African-Americans.

Rumain Brisbon, a 34-year-old drug suspect, was shot dead by an officer after a scuffle in Phoenix, Arizona.

The fatal incident came a day before a New York City grand jury's decision not to indict Officer Daniel Pantaleo, who is white, in the chokehold death of Eric Garner, an unarmed black man, sparked massive protests.

Last week, unrest was triggered by another Grand Jury decision, this time in Ferguson, Missouri, not to charge police officer Darren Wilson for the death of unarmed black teenager, Michael Brown.

Brisbon's death also resulted in about 150 demonstrators rallying through the streets of Phoenix to police headquarters, calling a more equal justice system.

Phoenix police said the police officer was investigating to a tip-off about someone selling drugs out of a vehicle when he saw Brisbon exit the car and ordered him to show his hands.

Brisbon instead fled towards a nearby an apartment building. The officer followed and a fight ensued.

"During the struggle, Brisbon put his left hand in his pocket and the officer grabbed on to the suspect's hand, while repeatedly telling the suspect to keep his hand in his pocket," a police spokesman said, The Washington Post reported.

"The officer believed he felt the handle of a gun while holding the suspect's hand in his pocket."

The policemen fired two shots and Brisbon, an ex-convict, was killed. Later, detectives said a semi-automatic handgun and a jar of marijuana were found in his car. The object in his pocket was revealed to be a bottle of pills.

"What happened here is a police officer murdered my client," Brisbon's attorney Marci Kratter told The Post. "If the officer felt a pill bottle and believed it was a butt of a handgun, it calls into question his competence because I don't know anyone who can mistake a plastic bottle for a butt of a gun. How much larger is a gun than a pill bottle?"