SAN FRANCISCO -- Federal prosecutors unsealed a 52-count indictment Thursday, charging 29 alleged members and associates of the notorious MS-13 gang with murder, attempted murder, alleged drug and firearms trafficking, robbery, assault and other violent crimes.

Arrests were made in San Francisco, Richmond, Oakland, Alameda, South San Francisco, San Bruno and Reno, Nev., according to U.S. Immigration and Customs Enforcement.

The indictment of the 29 suspected members or associates of the gang was unsealed by U.S. Attorney Joseph Russoniello, who discussed "Operation Devil Horns" -- a reference to the MS-13 gang sign -- at a news conference in San Francisco.

While some of those indicted were arrested during the ICE raids, others were already in prison on other charges, according to ICE.

Marcy Forman, ICE's national office of investigations director, said the charges represented the "largest criminal indictment of MS-13 gang members in U.S. history."

MS-13, also known as Mara Salvatrucha, originated in El Salvador and Southern California, and has members throughout the Bay Area in the thousands, according to Russionello. He called the group "one of the most vicious, dangerous organized crime gangs" in the country, and said its members engaged in "indiscriminate violence" against innocent victims as well as other gangs and its own members.

Russionello said the arrests, which included alleged leaders of the gang, would have a significant impact, but represented a "continuing struggle" against the group's spread.

"With each victory that we achieve, it makes it more difficult for them to replenish," he said.

"They're not all going to be leaving town tomorrow," Russionello said, "but they may now be distrustful of their own members."

The operation, which began in 2005, included undercover ICE agents monitoring the gang's illegal activities.

The indictment charged 22 alleged gang members with offenses in the aid of racketeering that included murder, attempted murder, assault, robbery, extortion, witness tampering, drug trafficking and interstate transportation of stolen vehicles. The suspects were alleged to be MS-13 members based in San Francisco's Mission District and the city of Richmond.

Three of those charged were linked to murders in San Francisco on July 11 and July 31 of this year.

On July 11, 31-year-old Armando Estrada, of Rodeo, was fatally shot in broad daylight at 20th and Mission streets, according to San Francisco police. That intersection is considered the territory of MS-13's "20th Street" clique.

Guillermo Herrera, aka "Shorty" or "Sparky," was named in the federal indictment for the July 11 murder.

On July 31, 14-year-old Ivan Miranda, of San Francisco, was stabbed to death during a confrontation with four other boys in the city's Excelsior District, according to police.

Walter Chinchilla-Linar, aka "Demonio," and Cesar Alvarado, aka "Momia," were named in the indictment for robbery and murder in connection with the July 31 attack.

Russionello said sentences for those convicted under federal racketeering charges run from 10 years in federal prison to life without parole. Those released after their sentences would then be deported.

Six other men and one woman were charged with non-racketeering offenses that also included drug and firearms trafficking, and attempting to export stolen vehicles.

Russionello called the effort "one more steady step in the process of taking back our communities."

"We have to be able to provide some alternatives to young people," he said.

Residents, community groups and immigration rights attorneys have expressed dismay, however, at the ICE raids.

Russionello acknowledged Wednesday's raids were "aggressive operations" but was unapologetic.

He said authorities pursuing criminal suspects "may not be in the most sensitive or compassionate mode."

"Yes, doors will be knocked down," he said. "Yes, guns will be drawn."

"But wherever possible, these officers ... are sensitive to the considerations of innocent persons," said Russionello.

However, if while serving warrants, immigration authorities suspect others there to be in the country illegally, they will also be detained and subject to deportation proceedings, according to ICE.