Nearly all of the members and associates of an MS-13 gang charged in the “medieval-style” slayings of seven people in California were in the country illegally, officials said.

The U.S. Attorney's Office in Los Angeles charged 22 people linked to a subset of the vicious gang that's known as the Fulton clique, members of which are suspected in nearly 200 crimes in several states over 9 years, according to a federal indictment released Tuesday.

"We have now taken off the streets nearly two dozen people associated with the most violent arm of MS-13 in Los Angeles," U.S. Attorney Nick Hanna said.

Of the 22 defendants, 19 had entered the country illegally in the past three or four years, according to Thom Mrozek, a spokesman for the U.S. Attorney's office in Los Angeles.

PROSECUTORS ACCUSE MS-13 OF 7 'MEDIEVAL-STYLE' SLAYINGS, INCLUDING CUTTING HEART OUT OF RIVAL

Federal prosecutors allege the suspects operated in the San Fernando Valley, an area that recently absorbed an influx of young immigrants from Central America.

"Under the influence of these young gangsters, younger associates who wanted to become members of MS-13 were 'required to kill an MS-13 rival or someone perceived to be adverse to MS-13 to be initiated into MS-13,' according to the indictment," the U.S. Attorney's Office said Tuesday.

"In Los Angeles, a clique added new members through an initiation ritual known as 'jumping in,' during which several existing MS-13 members beat up a prospective MS-13 member for 13 seconds while the shot caller counted aloud for 13 seconds," the indictment read. "Beginning in 2017 in Los Angeles, MS-13 members who identified with '503' had been required" to murder a rival or other enemy of the group.

Authorities said "503" represents the sub-group of MS-13 and is the telephone country code for El Salvador.

The brutality involved in some of the alleged killings was also disclosed in graphic detail by authorities. Four of the killings took place in Angeles National Forest. The slayings were carried out using machetes, bats and knives, according to the indictment.

In one case a member of a rival gang who had been believed to have defaced MS-13 graffiti was targeted and had his heart cut out of his chest, authorities said.

On March 6, 2017, the victim, identified as “J.S.,” was driven to Angeles National Forest, where six MS-13 gang members attacked him with a machete, killing him, the indictment claimed.

“The victim was dismembered and his body parts were thrown into a canyon after one of the defendants allegedly cut the heart out of the victim’s body,” a news release from Hanna’s office said.

"Taking violent offenders off the street should send a message to MS-13 members and their associates that medieval-style violence and senseless murder will not be tolerated in Los Angeles," said Paul Delacourt, assistant director in charge of the FBI's Los Angeles field office.

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Hanna released photos showing MS-13 members displaying a machete, gang signs and guns in various poses.

Sixteen of the 22 people indicted are charged in connection with six slayings, which officials said were so "heinous, cruel or depraved" that the defendants are eligible for the death penalty. Prosecutors have not said whether they intend to seek capital punishment, however.

All 22 of the alleged MS-13 members and associates are in custody. Eighteen had been apprehended during the last year on a range of federal and state charges, authorities said. Three were arrested in recent days in the Los Angeles area by a task force that included FBI agents, Los Angeles police officers and Los Angeles County sheriff's deputies. Another alleged MS-13 affiliate was arrested over the weekend in Oklahoma.

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Authorities also filed two more cases under seal against juvenile defendants in federal court.

"The collaborative law enforcement effort solved several murder cases and dealt a severe blow to members of the gang who engaged in acts of brutality not seen in the region for over 20 years," Hanna said.

Fox News' Robert Gearty and The Associated Press contributed to this report.