Media playback is unsupported on your device Media caption Protester: "If it had been a white boy who had been murdered, and a black guy who had murdered him, would they have acquitted him?"

Protests have taken place across the US after neighbourhood watch volunteer, George Zimmerman, was cleared of murdering an unarmed black teenager.

Most demonstrations were peaceful, demanding justice for the family of 17-year-old Trayvon Martin and questioning the fairness of the justice system.

The biggest protest was in New York, where a small rally grew into a crowd of thousands.

President Barack Obama has appealed for calm reflection after the verdict.

He acknowledged on Sunday that the case had elicited "strong passions", but said: "We are a nation of laws, and a jury has spoken."

The Department of Justice says it is investigating whether a civil case can now be brought against Mr Zimmerman.

The 29-year-old neighbourhood watch volunteer had faced charges of second-degree murder and manslaughter due to his fatal shooting of the teenager last year.

'Angry, scared, anxious'

Image caption The rally in Times Square was peaceful, but people were clearly very angry at the verdict

After the not-guilty verdict was announced late on Saturday, there were protests in cities across the US - including in San Francisco, Philadelphia, Chicago, Washington, Boston, San Diego and Atlanta.

In New York City, thousands of people marched to Times Square on Sunday night, chanting "Justice for Trayvon Martin!''

Police attempted to keep the crowd in controlled lanes, but the demonstrators made their way around the officers into the square.

Derreck Wilson, 46, who came to Times Square from the traditionally African-American neighbourhood of Harlem, said protesters were there "to say in a peaceful way why we are angry. We are angry, scared and anxious."

In San Francisco, protester Rand Powdrill, 41, said he came to march with about 400 others to "protest the execution of an innocent black teenager".

"If our voices can't be heard, then this is just going to keep going on," he said.

In Los Angeles, protesters blocked traffic, and several roads were closed.

Police said most of the protesters were peaceful, but several splinter groups were more aggressive, reportedly throwing rocks and batteries at police at one location.

Los Angeles Mayor Eric Garcetti urged protesters there to "practise peace".

Later on in the evening, about 80 protesters gathered in Hollywood on Sunset Boulevard, near the CNN bureau.

According to the Los Angeles Times, more than 100 police officers converged on the crowd, declaring an unlawful assembly and ordering them to disperse before making arrests.

Seven arrests were made across the city on Sunday and early into Monday.

In Boston, about 500 protesters marched alongside police escorts. "They've been very orderly," Boston police superintendent William Evans told reporters.

Trayvon Martin was also remembered in many church services across the country on Sunday.

"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 Raphael Warnock, the senior pastor at Ebenezer Baptist Church in Atlanta, told his congregation.

'Honouring' Trayvon

On Sunday US President Barack Obama called for "calm reflection" over the incident.

He said Trayvon Martin's death was a tragedy for America, but that it was "a nation of laws and a jury has spoken".

"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... As citizens, that's a job for all of us.

"That's the way to honour Trayvon Martin."

Mr Obama had commented on the Zimmerman case in March last year, saying: "If I had a son, he'd look like Trayvon."

Media playback is unsupported on your device Media caption Residents of Sanford, Florida, give their reaction to the clearing of George Zimmerman

Civil rights leader Jesse Jackson told CNN on Sunday that "the American legal system has once again failed justice".

But he also appealed for calm, saying anyone seeking to "compound our pain with street justice" would do "damage to the innocent blood and legacy of Trayvon Martin".

Rights activist and broadcaster Al Sharpton said the verdict was "a slap in the face to the American people".

He compared the case to the beating of African-American man Rodney King by police in 1991, which sparked widespread rioting.

Mr Zimmerman's family and representatives have said they are afraid he could fall victim to revenge attacks.

His brother Robert said he had received frequent threats on social media and there was "more reason now than ever to think that people are trying to kill him".

"He's going to be looking over his shoulder the rest of his life," he said.

His lawyer, Mark O'Mara, told ABC News on Sunday that Mr Zimmerman had no regrets about having carried a gun on the night of 26 February 2012.

He said his client would now be entitled to have his weapon returned to him and to carry it, saying there was "ever more reason now, isn't there? There are a lot of people out there who actually hate him, though they shouldn't."

Jorge Rodriguez, a friend of Mr Zimmerman's, said he had told him of his relief. He told Reuters he did not understand the anger at the verdict.

"Everybody asked for justice, and they got it."

In a statement, the justice department said they were continuing to evaluate the evidence in their open investigation of Martin's death.

The department has a long history of using federal civil rights law in an effort to convict defendants who have previously been acquitted in related state cases, but convictions are often tough to obtain in such cases, analysts say.

Federal prosecutors "would have to show not only that the attack was unjustified, but that Mr Zimmerman attacked Mr Martin because of his race and because he was using a public facility, the street," Alan Vinegrad, a former US Attorney, told the Associated Press.