The response by law enforcement to protesters in Ferguson, Mo., is being criticized for its level of force and use of military-style equipment. We've labeled the weapons and gear being used by police in these photos from Ferguson. (Tom LeGro and Thomas Gibbons-Neff/The Washington Post)

Federal and state officials unveiled a sweeping response Thursday to violent clashes between police and protesters over the shooting death of an unarmed black teenager, with Missouri taking over security operations from local police and authorities agreeing to accept Justice Department help in handling protests.

Speaking from Martha’s Vineyard, Mass., where he is on vacation, President Obama called for national unity following the police shooting Saturday of Michael Brown, 18, in this St. Louis suburb. “Now is the time for peace and calm on the streets of Ferguson,’’ Obama said. “Let’s remember that we’re all part of one American family.’’

Attorney General Eric H. Holder Jr. then announced a series of steps his department is taking, including a meeting held Thursday with civic leaders to calm tensions and an escalating civil rights probe in which federal investigators have already interviewed witnesses to the shooting.

In unusually blunt remarks, Holder said that he was “deeply concerned” about “the deployment of military equipment and vehicles’’ on Ferguson’s streets and that Missouri officials have accepted federal assistance “to conduct crowd control and maintain public safety without relying on unnecessarily extreme displays of force.’’

Even as dozens of protesters continued their campaign near the shooting scene for a fifth day on Thursday, state officials followed the federal lead. Missouri Gov. Jay Nixon (D) announced that the Missouri State Highway Patrol would take over security operations in Ferguson, led by Capt. Ronald S. Johnson, an African American who grew up in the area. “We are going to have a different approach and have the approach that we’re in this together,” Johnson said.

As a result, the heavy riot armor, the SWAT trucks with sniper posts and the gas masks were gone from the streets of Ferguson Thursday night, and Johnson marched with the crowd, eliciting cheers from the protesters. Johnson vowed to not blockade the streets, to set up a media staging center, and to ensure that residents’ rights to assemble and protest were not infringed upon.

“I’m not afraid to be in this crowd,” Johnson declared to reporters.

Obama’s remarks were the most visible step in a rapid coalescence among political and community leaders to tamp down the violence, as images of riot police, tear gas and government intervention provoked a national debate about race and justice that recalled civil rights battles of a half-century ago.

In a sudden burst of interest fueled by photos and video of heavily armed police that swirled on social media, politicians from both sides of the aisle rushed on Thursday — five days after the shooting — to condemn the tactics of the nearly all-white police force in the predominantly African American town.

The reactions were remarkably similar across the political spectrum. Sen. Claire McCaskill (D-Mo.), for example, called for authorities to “de-militarize this situation,’’ while Sen. Rand Paul (Ky.), a likely Republican presidential candidate, condemned “the militarization of our law enforcement’’ in a Time magazine essay.

But on the ground in Ferguson, the support from politicians at all levels was met with skepticism, and it was unclear how much effect it would have.

Eddie Hasan, a St. Louis resident who helped organize a forum Thursday night at a local Baptist church for young people to voice their concerns, called on elected officials to play a greater role in calming tensions. “This forum, this chance for the youth to speak out absolutely should have happened sooner,” he said. “Hopefully it helps us get some resolution to the issue.”

State Sen. Maria Chappelle-Nadal, who has been active in planning recent protests and was tear-gassed Monday, said local and state officials have been woefully absent. “There hasn’t been a single white Democrat down here,” Chappelle-Nadal, who represents Ferguson, said on Wednesday before Nixon’s visit. “Mark my words, the Republicans might start showing up before they do.”

Underlying the dispute was the continuing lack of clarity about just what happened Saturday night in Ferguson.

According to a friend who says he witnessed the incident, Brown was walking down a Ferguson street when a police officer in a car ordered him to get on the sidewalk. Brown had his hands in the air to show he was unarmed when the officer shot him multiple times, the friend said.

The police version is that Brown attacked the officer in his car and tried to grab his gun. Ferguson Police Chief Thomas Jackson said during a news conference on Wednesday that the officer was struck in the face during the encounter. The side of the officer’s face was “swollen,” Jackson said, and he was treated at a hospital.

Federal investigators are still trying to sort out the conflicting versions of events but are proceeding cautiously and deferring to state investigators for now, a federal law enforcement official said Thursday. The official, speaking on condition of anonymity to discuss an ongoing investigation, said the investigation is a high priority for the Justice Department and FBI but it is far too early to determine if any charges will be brought.

The Justice Department’s civil rights division, along with the U.S. attorney’s office in St. Louis and the local FBI field office, are investigating the shooting to determine if anyone’s civil rights were violated. The federal probe is running parallel to the state investigation.

Holder, who met with Obama on Thursday to discuss the case, said: “Our review will take time to conduct, but it will be thorough and fair.”

Another source of frustration for residents is that police, who initially promised to identify the officer involved in the shooting, have backtracked because of what they say are threats to his safety.

The lack of specifics about the shooting, combined with anger over the show of police force, has many protesters vowing to continue their campaign. Dozens of people did so on Thursday near the shooting scene and also outside the Ferguson police station.

On the fourth day of demonstrations, the crowds still rivaled the size at comparable points on previous days, with dozens standing around the burned-out QuikTrip convenience store and half a dozen or so on the center divider — with one man laying face down in the street and the others pointing their fingers like guns at him.

“Hands up, don’t shoot!” they declared, words that have been the soundtrack of Ferguson’s unrest.

Many residents said that they do not care if elected officials ever show up. “I don’t want to see any governors, or any mayors, or even any more cameras,” said Derrick Beavers, 32, a protester who said he knew Brown. “I want justice.”

In Massachusetts, Obama also called on federal officials to ensure “that justice is done.”

“There is never an excuse for violence against police or for those who would use this tragedy as a cover for vandalism or looting,” the president said, adding: “There is also no excuse for police to use excessive force against peaceful protests or to throw protesters in jail for lawfully exercising their First Amendment rights.’’

In concluding his remarks, Obama said that while “emotions are raw right now” in the suburb and accounts of the tragedy differ, “Now is the time for healing. Now is the time for peace and calm on the streets of Ferguson. Now is the time for an open and transparent process to see that justice is done. And I’ve asked the attorney general and the U.S. attorney on the scene to continue to work with local officials to move that process forward.”

Obama did not take questions from reporters after his remarks.

In Missouri, Nixon said the highway patrol would assume operational control of the law enforcement response to protests but that local officers from Ferguson and the county police would remain involved, as they have been all week.

When Johnson took the podium, it seemed clear that things had changed, at least rhetorically. “I understand the anger and fear that the citizens of Ferguson are feeling, and our officers will respect both of those,” said Johnson, who has been the head of the highway patrol’s troopers in the region since 2002.

Johnson vowed that he would be on the ground himself on Thursday night and said he planned to visit the QuikTrip store that has become ground zero for the protesters.