Barack Obama made his first public remarks on the killing of Trayvon Martin, saying that the Florida teenager's death was a "tragedy" that needed to be fully investigated.
In a personal message delivered from the White House, the US president likened Trayvon Martin to his own children, and said: "If I had a son, he would look like Trayvon".
Obama vowed that authorities would look into "every aspect" of the shooting of the unarmed 17-year-old by neighbourhood watchman George Zimmerman, and called on federal, state and local authorities to work together as part of the investigation.
Martin was killed on February 26 in circumstances that have yet to be fully explained. Although Zimmerman admits he killed the teenager, he says it was in self-defence, citing Florida's controversial "stand your ground" law that allows the use of lethal force in certain circumstances. Zimmerman has not been arrested, sparking growing anger that has spread beyond Florida.
Obama's intervention was prompted by a question from reporters during a White House announcement on its nominee for head of the World Bank.
"Obviously this is a tragedy. I can only imagine what these parents are going through," he said from the White House Rose Garden.
"When I think about this boy, I think about my own kids, and I think every parent in America should be able to understand why it is absolutely imperative that we investigate every aspect of this."
Obama said that all of America had some "soul searching" to do over the incident, adding: "If I had a son he would look like Trayvon and I think they [his parents] are right to expect that all of us as Americans are going to take this with the seriousness it deserves."
Republican presidential candidate Mitt Romney later joined the president in calling for a "thorough investigation". He added that a full inquiry was needed so that "justice is carried out with impartiality and integrity".
Meanwhile, Fox News commentator Geraldo Rivera sparked outrage on Friday when he claimed that Martin was singled out for attention because he was wearing a hoodie.
Calling on parents of black and Latino youngsters to prevent their children going out onto the streets in hooded sweatshirts, Rivera added: "I think the hoodie is as much responsible for Trayvon Martin's death as George Zimmerman was".
The statement received an immediate backlash online, as critics took to twitter to vent their anger. Rivera later tweeted that his son had messaged him to say he was ashamed of his position.
The focus on black and Latino youths by Rivera also reinforced the view held by some that the incident may have had a racial element to it.
Sanford's police chief Bill Lee stepped down temporarily on Thursday. The announcement was followed by news that Florida state attorney Norman Wolfinger had also recused himself following criticism of his handling of the case. But neither move appeared to soothe the growing discontent or quieten calls for Zimmerman to be arrested.
On Thursday night a rally was held in Sanford, the city in which Martin was shot dead as he returned to the home of his father's girlfriend after a trip to a local convenience store.
At the demonstration, the 17-year-old's parents, Tracy Martin and Sybrina Fulton, were joined by civil rights leaders including the Rev Al Sharpton.
Sharpton told those gathered: "We cannot allow a precedent when a man can just kill one of us and then walk out with the murder weapon. We want George Zimmerman in court with handcuffs behind his back."
