Missouri state police will take over supervising security from local police in the St. Louis suburb that's been the scene of violent protests since a white police officer fatally shot an unarmed black teenager, the governor announced Thursday. A new protest with hundreds of people began hours later.

President Barack Obama has appealed for "peace and calm" on the streets of Ferguson, the predominantly black city where crowds have gathered to protest since Saturday's shooting of 18-year-old Michael Brown.

Gov. Jay Nixon announced that state Highway Patrol Capt. Ron Johnson, who is black, will take over security after the local police response drew heavy criticism. Nixon said the change is intended to make sure "that we allow peaceful and appropriate protests, that we use force only when necessary, that we step back a little bit and let some of the energy be felt in this region appropriately."

Nixon's promise to ease the deep racial tensions was swiftly put to the test as demonstrators gathered again Thursday evening in the neighborhood where looters smashed and burned businesses on Sunday and police repeatedly fired tear gas and smoke bombs.

Johnson said he grew up in the community and "it means a lot to me personally that we break this cycle of violence." He said he planned to keep heavily armored vehicles away from the scene and told his officers not to bring their tear gas masks.

By late afternoon, Johnson was walking down the street with a group of more than 1,000 protesters as they chanted "Hands up, don't shoot," a reference to witness accounts that described Brown as having his hands in the air when the officer kept firing.

Johnson planned to talk to the demonstrators throughout the night.

"We're going to have some conversations with them and get an understanding of what's going on."

Obama, speaking from the Massachusetts island where he's on a two-week vacation, said there was no excuse for excessive force by police in the aftermath of the shooting. He said he had asked the Justice Department and FBI to investigate the incident.

"I know emotions are raw right now in Ferguson, and there are certainly passionate differences about what has happened," Obama said. "But let's remember that we're all part of one American family. We are united in common values, and that includes the belief in equality under the law, respect for public order and the right to peaceful public protests."

St. Louis County police spokesman Brian Schellman said officers on Wednesday night tossed tear gas to disperse a large crowd of protesters after some threw Molotov cocktails and rocks at officers. More than 10 people were arrested in Ferguson.

Residents in Ferguson have complained about the police response that began soon after Brown's shooting with the use of dogs for crowd control — a tactic that for some evoked civil-rights protests from a half-century ago. The county police force took over, leading both the investigation of Brown's shooting and the subsequent attempts to keep the peace at the smaller city's request.

County Police Chief Jon Belmar said his officers have responded with "an incredible amount of restraint" as they've had rocks and bottles thrown at them, been shot at and had two dozen patrol vehicles destroyed.

The city and county are also under criticism for refusing to release the name of the officer who shot Brown, citing threats against that officer and others. The hacker group Anonymous on Thursday released a name purported to be that of the officer, but the Ferguson police chief said later that the name was incorrect.

Twitter quickly suspended the Anonymous account that posted the officer's purported identity and personal information. The site's code of conduct strictly forbids the publication of private and confidential information without permission.

Police have said Brown was shot after an officer encountered him and another man on the street. They say one of the men pushed the officer into his squad car, then physically assaulted him in the vehicle and struggled with the officer over the officer's weapon. At least one shot was fired inside the car. The struggle then spilled onto the street, where Brown was shot multiple times.

The officer involved was injured, with one side of his face swollen, Ferguson Police Chief Thomas Jackson said.

Dorian Johnson, who says he was with Brown when the shooting happened, has told a much different story. He has told reporters that the officer ordered them out of the street, then grabbed his friend's neck and tried to pull him into the car before brandishing his weapon and firing. He says Brown started to run and the officer pursued him, firing multiple times.

Johnson and another witness both say Brown was on the street with his hands raised when the officer fired at him repeatedly.

Attorney General Eric Holder has said federal investigators have interviewed eyewitnesses to the shooting. A person familiar with the matter, who spoke on condition of anonymity because the investigation is ongoing, said federal authorities have interviewed Johnson.

Holder spoke by telephone Thursday with Brown's family to offer condolences and to tell them that the Justice Department was committed to a full and independent investigation.