George Zimmerman verdict: Obama calls for 'calm reflection' amid protests (VIDEO)

Thousands of people took to the streets across the United States on Sunday to protest the acquittal of George Zimmerman for fatally shooting Trayvon Martin, prompting President Barack Obama to call for "calm reflection."

Demonstrators in New York, Los Angeles, Chicago, San Francisco and other cities demanded "Justice for Trayvon" after a jury on Saturday found Zimmerman not guilty of murdering the unarmed black teenager in a Florida town last year. 

Zimmerman's lawyers successfully argued that the neighborhood watch volunteer shot Martin, 17, in self-defense. Many civil rights activists, however, believe that the shooting was racially motivated.

"Trayvon Benjamin Martin is dead because he and other black boys and men like him are seen not as a person but a problem," the Rev. Dr. Raphael G. Warnock, senior pastor at the Ebenezer Baptist Church in Atlanta that Martin Luther King Jr. once led, told his congregation, according to the New York Times.

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A crowd of thousands descended on New York's Times Square Sunday evening, the Times reported, bringing traffic to a standstill at one of the city's biggest intersections. 

In LA, protesters blocked parts of the 10 Freeway as rallies broke out across the city. There were clashes and one arrest as some demonstrators threw stones and batteries at police, the Los Angeles Times said, but the police department stressed that most protests remained peaceful.

There were smaller marches and vigils in several other cities, the Associated Press reported, including Chicago, Washington DC, Miami, where Martin was from, and Sanford, where he was shot and where Zimmerman was tried.

Obama acknowledged that passions were running high after Martin's death — which he called "a tragedy" for all America — and now Zimmerman's acquittal, but said the jury had spoken and it was time to look ahead.

More from GlobalPost: 'Justice for Trayvon' shouts echo after Zimmerman acquittal

"We should ask ourselves if we're doing all we can to stem the tide of gun violence that claims too many lives across this country on a daily basis," the president said in a statement

"We should ask ourselves, as individuals and as a society, how we can prevent future tragedies like this. [...] That's the way to honor Trayvon Martin."

The Justice Department has said it is studying whether there are grounds to bring criminal civil rights charges against Zimmerman in a federal court. 

"We will pursue civil rights charges with the Department of Justice, we will continue to fight for the removal of stand-your-ground laws in every state, and we will not rest until racial profiling in all its forms is outlawed," said a statement from the National Association for the Advancement of Coloured People (NAACP), which has started a petition to ask federal prosecutors to pursue the case.