United States attorney-general Eric Holder has called for a rethink of controversial "stand-your-ground" laws following the acquittal of a neighbourhood watch volunteer who fatally shot an unarmed black teenager in Florida.

Mr Holder acknowledged the anger stirred across the country by the racially-tinged trial of George Zimmerman, 29, found not guilty on Saturday of murdering 17-year-old Trayvon Martin.

"Separate and apart from the case that has drawn the nation's attention, it's time to question laws that senselessly expand the concept of self-defence and sow dangerous conflict in our neighbourhoods," Mr Holder told a meeting of the National Association for the Advancement of Coloured People (NAACP) in Orlando, Florida.

"These laws try to fix something that was never broken," he said. "There has always been a legal defence for using deadly force if - and the "if" is important - no safe retreat is available."

Mr Zimmerman's trial lawyers did not explicitly invoke Florida's stand-your-ground law, arguing instead that he acted in self-defence in a confrontation with Martin in February last year.

But the case has stirred up controversy around such laws, present in some 30 states, which assert that citizens can use lethal force - rather than retreat - if they sense their lives are threatened, wherever they might be.

"By allowing and perhaps encouraging violent situations to escalate in public, such laws undermine public safety," Mr Holder said.

"The list of resulting tragedies is long and unfortunately has victimised too many who are innocent.

"It is our collective obligation - we must 'stand our ground' - to ensure that our laws reduce violence and take a hard look at laws that contribute to more violence than they prevent."

Critics of the verdict from the six-woman and mostly white jury argue that Mr Zimmerman had racially profiled Martin - who had no criminal record - and was able to kill him with impunity because of a biased criminal justice system.

Government urged to pursue civil proceedings

Meanwhile, pressure grew yesterday for Mr Zimmerman to face civil proceedings, with African-American faith leaders led by civil rights firebrand Reverend Al Sharpton announcing protest rallies on Saturday in more than 100 cities.

"People all over the country will gather to show that we are not having a two- or three-day anger fit," Reverend Sharpton told reporters outside the Justice Department headquarters in Washington.

"This is a social movement for justice."

Mr Holder remained non-committal on whether the Justice Department might pursue Mr Zimmerman on civil rights grounds.

"The Justice Department has an open investigation" into the case, he said.

"While that inquiry is ongoing, I can promise that the Department of Justice will consider all available information before determining what action to take."

Police vow to clamp down on protests

In Los Angeles, police chief Charlie Beck vowed to clamp down harder on protests over the outcome of the Martin trial, after 14 people were arrested on a second night of violence.

"We cannot allow a small group of individuals to not only damage ... and strike fear in the community, but also to destroy the message of so many in the community," he said.

In Houston, police on horseback watched from the sidelines as protesters marched outside the city's downtown federal court house, the Houston Chronicle newspaper reported on its website.

One of the jurors who acquitted Mr Zimmerman meanwhile scrapped controversial plans to write a book about the trial, explaining that she had not been aware of how deeply it had aroused passions.

"I realise it was necessary for our jury to be sequestered in order to protest our verdict from unfair outside influence," the woman, known only as juror B-37 said.

"But that isolation shielded me from the depth of pain that exists among the general public over every aspect of this case.

"Now that I am returned to my family and to society in general, I have realised that the best direction for me to go is away from writing any sort of book and return instead to my life as it was before I was called to sit on this jury."

Stevie Wonder refuses to perform

Pop music icon Stevie Wonder declared he would refuse to perform in Florida or any other state with a so-called stand-your-ground law.

The black Rock and Roll Hall of Fame enshrinee made his comments at a concert on Sunday in Quebec City, Canada, according to a video posted on YouTube.

"For the gift that God has given me, and for whatever I mean, I decided today that until the 'stand-your-ground' law is abolished in Florida, I will never perform there again," Mr Wonder said.

He did not mention the Zimmerman trial by name in the video-clip posted online.

AFP/Reuters