Obama gets personal over killing of black Florida teenager

US President Barack Obama weighed into the controversial killing of a black teenager in Florida in very personal terms on Friday, comparing the boy to a son he doesn't have and calling for US "soul searching" over how the incident occurred.

Seventeen-year-old Trayvon Martin, dressed in a "hoodie" sweatshirt, was shot dead a month ago in Sanford, Florida by a 28-year-old white Hispanic neighbourhood watch volunteer who said he was acting in self-defence.

"If I had a son, he'd look like Trayvon," Obama said in his first comments about the shooting, acknowledging the racial element in the case.

"Obviously, this is a tragedy," Obama told reporters. "I can only imagine what these parents are going through. And when I think about this boy, I think about my own kids."

The case has rippled across the nation and prompted rallies protesting the failure of the police to arrest the shooter, George Zimmerman, and, more broadly, a pattern of racial discrimination black leaders cite in Sanford and elsewhere in the country.

Obama, the first black US president, made his remarks at a White House event to announce his pick to lead the World Bank, waiting briefly after the announcement to take a reporter's question about the incident.

Martin's parents thanked the president for his words.

"The president's personal comments touched us deeply and made us wonder: If his son looked like Trayvon and wore a hoodie, would he be suspicious too?," they said in a statement.

Florida's "Stand Your Ground" law allows people to use deadly force in self-defence.

Similar laws are in effect in at least 24 states including Florida, according to the Brady Campaign to Prevent Gun Violence. Calls are mounting to repeal them. Earlier this week, a Florida state senator said he was drafting new legislation to drastically change the law in Florida.

A South Carolina state representative said on Friday he had introduced a bill to repeal his state's law. Bakari Sellers, a black Democrat and gun owner, said he wanted to prevent an incident like the Trayvon Martin shooting happening in his state.

"I'm six-five and a black guy," he said. "I just know that it could have been me."

Obama said the "Stand Your Ground" laws should be studied.

"I think all of us have to do some soul-searching to figure out how does something like this happen. And that means that examine the laws and the context for what happened, as well as the specifics of the incident," he said.

"Every parent in America should be able to understand why it is absolutely imperative that we investigate every aspect of this, and that everybody pulls together -- federal, state and local -- to figure out exactly how this tragedy happened."