Similar rallies have been held in dozens of American cities, including New York City, Chicago, Philadelphia, Miami and Minneapolis. 

Demonstrations in New York and Missouri started out peacefully on Wednesday, calling for police reforms after a grand jury decided not to indict a white New York police officer who choked unarmed black man Eric Garner to death in July.

The protests came amid angry demonstrations against the death of African-American teenager Michael Brown, who shot dead by white police officer Darren Wilson in Ferguson in August. 

Wilson walked free after Saint Louis County prosecutor Robert McCulloch said he would not be indicted.  

The killings have highlighted the strained relations between police and African-Americans and rekindled a national debate over race relations in the United States.

Unlike the fatal shooting of Brown, the chokehold death of Garner was recorded on videos that have been widely seen and have contributed to the public outrage. In the video, Garner repeatedly told police officers I can't breathe! I can't breathe!

US police shoot and kill an average of 1,000 people a year, 1 in 4 of whom unarmed, according to a report by the Police Policy Studies Council.

Based on a recent study by the Malcolm X Grassroots Movement, 313 black people were killed in 2012 by police officers, private security guards and members of the public and in most cases, the perpetrator was not indicted.