FERGUSON, Mo. -- The police chief in a Missouri city where a police officer fatally shot an unarmed black teenager said Tuesday he's holding off on publicly identifying the officer because of death threats.

Civil rights leader Al Sharpton, standing with the parents of 18-year-old Michael Brown, criticized the decision, saying the secrecy is fueling mistrust of the police in Ferguson, a predominantly black city of about 21,000 residents where violent protests broke out following the shooting.

Investigators have released few details, saying only that a scuffle unfolded after the officer asked Brown and another teen to get out of the street. At some point, the officer's weapon fired inside a patrol car, police said. Witnesses have said that Brown had his hands raised when the officer approached with his weapon and repeatedly fired.

President Barack Obama, who is vacationing on the Massachusetts island of Martha's Vineyard, said that while the case has prompted "strong passions," people should remember Brown through "reflection and understanding." He called on people to comfort each other "in a way that heals, not in a way that wounds."

Missouri Gov. Jay Nixon told people at a community forum Tuesday night that the shooting feels "like an old wound torn fresh" in a nation still struggling with race relations.

The forum was organized as an alternative response to two nights of unrest in which crowds have burned stores, vandalized vehicles, assaulted reporters and taunted officers. Ferguson's mayor and police chief also attended the meeting and were welcomed with applause.

Police said death threats prompted them to withhold the name of the officer, who was placed on administrative leave after the shooting.

"The local authorities have put themselves in a position -- hiding names and not being transparent -- where people will not trust anything but an objective investigation," Sharpton, standing with Brown's mother and father, said during a news conference outside a St. Louis courthouse.

But he also echoed pleas by Brown's parents and the NAACP civil rights group for peaceful protests in Ferguson, where the case has stoked racial tension, protests and looting.

"I need all of us to come together and do this right," said Michael Brown Sr., with Sharpton standing at his side. "No violence."

Some civil rights leaders have drawn comparisons between Brown's death and that of 17-year-old Trayvon Martin, who was fatally shot by a Florida neighbourhood watch volunteer who was later acquitted of murder charges.

The case has provoked a broad discussion on social media sites about the death of young black men in racially tinged shootings. On Twitter, a campaign using the hashtag #IfTheyGunnedMeDown prompted many black users to post photos of themselves and ask how they might be portrayed in news reports if they became shooting victims.

Ferguson Police Chief Tom Jackson said he had planned to release the officer's name Tuesday but changed course after death threats were called into the police department and City Hall, and posted on social media. He said it could be weeks before he releases the name.

The race of the officer involved in the shooting also hasn't been disclosed, but witnesses said he was white. Brown was black.

The officer had been with the force for about six years and was on a routine patrol when he encountered the two young men, Jackson said.

The Ferguson police force has 53 officers, three of which are black. Jackson said the city has had trouble recruiting and retaining black officers.

Nearly three dozen people were arrested following a candlelight vigil Sunday night as crowds burned stores, vandalized vehicles, assaulted reporters and taunted officers. A large crowd that gathered Monday at a burned-out convenience store turned rowdy at nightfall, with people throwing rocks at police, Jackson said. Officers used tear gas and shot "beanbag rounds" meant to stun them.

There were at least five arrests from Monday's unrest but no reports of looting, said Brian Schellman, spokesman for the St. Louis County Police Department.