The parents of a black American teenager, shot dead by a neighbourhood-watch volunteer in Florida, have angrily denied that their son attacked first.

Reports alleged that the volunteer, George Zimmerman, fired his gun after he was punched and beaten by Trayvon Martin.

Florida's police have been under fire for weeks as protests decrying inaction in the case have spread to cities across the country.

More than two million people have signed an online petition calling for justice in the case, prompting Florida Governor Rick Scott to caution against a rush to judgment and say state authorities were still gathering facts.

"Justice will prevail," Mr Scott said in an interview with Reuters Insider in New York. "That's what we all want. We want the ... facts and we want to know that justice happens."

Investigators interviewed the teenager’s parents yesterday and questioned neighbours who lived near the shooting scene.

Trayvon Martin, a Miami high school student, was staying at the home of a friend of his father in Sanford, because he had been suspended from school shortly before his death.

Yesterday, a family spokesman said the 10-day suspension came after school officials discovered marijuana residue in a plastic bag inside Martin's schoolbag.

"Regardless of Trayvon's suspension, it had nothing to do with what happened on 26 February," Ryan Julison, the family spokesman, told reporters.

The teenager’s mother, Sybrina Fulton, suggested in comments at a news conference that the marijuana residue report was aimed at smearing her dead child.

"They've killed my son and now they're trying to kill his reputation," she said.

Civil rights leader Al Sharpton said Trayvon was being demonised in order to divert attention from Mr Zimmerman's actions.

"I said to the parents, as much as they were hurting, they will try to make your son a junkie, a thief, an assaulter and everything else before this is all over because they've done it in every case we've fought," Mr Sharpton said before entering a town hall meeting at the Sanford Civic Center.

Trayvon’s father, Tracy Martin, said he was not seeking revenge.

"We're not asking for an eye for an eye. We're asking for justice, justice, justice," he said at the meeting.

Newspaper publishes Zimmerman's claims

The account of Mr Zimmerman was published for the first time yesterday in the online edition of the Orlando Sentinel.

Police in Sanford, Florida, the Orlando suburb where the 17-year-old was shot dead have confirmed that the newspaper report appeared to be based on leaked information from someone inside the police department.

"The information in the article is consistent with the information provided to the State Attorney's office by the police department," the police said in a statement.

Mr Zimmerman, a 28-year-old white Hispanic, has been widely criticised for following the teenager, and ignoring a police request that he stop doing so after calling the 911 emergency number to report that the young man in a "hoodie" hooded sweatshirt looked to be "up to no good."

But in own his version of events, as outlined in the Sentinel report, Zimmerman had given up the chase and was walking back to his vehicle when the deceased approached him from behind.

The newspaper reported claims that the two exchanged words before Trayvon Martin punched Mr Zimmerman in the nose, sending him reeling to the ground. The teenager then began hitting him and slammed his head into the sidewalk several times.

At least one witness told police he saw Trayvon Martin on top of Mr Zimmerman who was calling for help, the newspaper said. It noted, however, that other witnesses had disputed from whom the cries were coming.

Mr Zimmerman has not been arrested.

Florida's "Stand Your Ground" law, which broadened the legal definition of self-defence when it was passed in 2005, provides people with immunity from detention or arrest if they use deadly force in their own defence without clear evidence of malice.