Federal authorities said on Sunday they were in contact with local police investigating the killing of a black teenager last month by a neighborhood watch volunteer at a gated Florida community, an incident that has raised alarm among civil rights leaders.

Police in Sanford, Florida, about 20 miles north of Orlando, have so far not charged George Zimmerman, 28, in the killing of Trayvon Martin on February 26 as the teen walked in the dark through the gated neighborhood, where he was visiting family.

Martin's family members have pressed for Sanford police to arrest Zimmerman in the shooting of the seventeen-year-old and have asked for state law enforcement and U.S. Justice Department intervention.

The FBI is "aware of the incident, we have been in contact with local authorities and are monitoring the matter," said Chris Allen, an FBI spokesman in Washington.

A spokeswoman for the Justice Department's civil rights division, which typically investigates incidents involving police, had no immediate comment.

The shooting has cast a spotlight on Florida's so-called "Stand Your Ground" law, which was passed under Governor Jeb Bush in 2005 and allows the use of guns or other deadly force in public places as a means of self-defense without first trying to retreat from a confrontation.

The law, copied by more than a dozen other states after it won passage in Florida, was pushed by theNational Rifle Association over protests from gun-control groups.

Pressure has mounted on federal authorities to take part in the investigation, following last week's release of recorded 911 emergency calls from the incident.

The Reverend Al Sharpton also has planned a rally for Thursday at a Sanford church to support the Martin family.

Zimmerman, who is white, has claimed the shooting was self-defense.

Zimmerman's father, Robert Zimmerman, said in a letter to the Orlando Sentinel that his son was a "Spanish speaking minority with many black family members and friends." He denied that Zimmerman followed or confronted Martin. "The portrayal of George Zimmerman in the media, as well as the series of events that led to the tragic shooting are false and extremely misleading."

Martin had taken a break from watching the NBA All-Star game on television to walk to a nearby convenience store to buy some Skittles candy for his 13-year-old brother, Chad, family lawyer Benjamin Crump told reporters earlier in March.

Martin, a high school junior who wanted to become a pilot, lived in Miami with his mother and had been staying for a few days at The Retreat at Twin Lakes in Sanford.

Sanford police received several calls from Zimmerman that day, including one about a suspicious person in the community as Martin returned from the convenience store.

Those recordings, reviewed by lawyers for Martin's family on Friday, and calls from other community residents posted by media, painted a picture of the scuffle that led to Martin's shooting.

Zimmerman had called police numerous times to report incidents in the months leading up to the shooting. That day he said there had been break-ins in the neighborhood and there was "a real suspicious guy" who "looks like he's up to no good."

The dispatcher asked Zimmerman if he was following the person. When Zimmerman replied that he was, the dispatcher said, "We don't need you to do that."

Area residents reported a scuffle in other emergency calls. In one recording - posted by the Orlando Sentinel and other media - a scream could be heard followed by the sound of a shot fired. In another recording two shots can be heard.

Late Friday, after police played 911 calls for them, lawyers for Martin's family told a news conference they planned to ask for a meeting with U.S. Attorney General Eric Holder.

Martin's parents told a news conference on Friday they had no trust in the Sanford police.

"I feel betrayed by the Sanford Police Department and there's no way that I can still trust them in investigating this crime," Martin's father, Tracy Martin, said.

Family attorney Crump called the 911 calls "shocking," and said Martin was shot in cold blood. The attorney said Zimmerman should be arrested immediately and called for federal authorities to take over the case.

"All the world is watching to see how this is going to conclude," Crump said.

In an opinion article in Sunday's The Miami Herald, Pulitzer prize winning columnist Leonard Pitts noted that Martin was shot and killed 60 years after Ralph Ellison published "Invisible Man," his seminal book about race relations in America.

Six decades later, a youth like Martin can still he deemed "suspicious" simply because "he existed while black," Pitts wrote.

Sanford Police Chief Bill Lee Jr. has defended the police handling of the case.

"The hysteria, the media circus, it's just crazy," Lee told the Orlando Sentinel. "It's the craziest damn thing I've ever seen, and it's sad. It's sad for the city of Sanford, the police department, because I know in my heart we did a good job."