OKLAHOMA CITY (CBSDFW.COM/AP) — Eighteen members of a white supremacist prison gang have been charged with racketeering, drug conspiracy and kidnapping that resulted in at least six homicides during the past 14 years, according to a federal indictment in Oklahoma.

The indictment, filed under seal in Tulsa on December 7 and unsealed Wednesday, says the 18 are members of the Universal Aryan Brotherhood, or UAB, described as a violent “whites only” gang based primarily in Oklahoma state prisons.

READ MORE: Fight Between Brothers Ends With 1 Shot, Critically Injured And 1 Arrested In Alvarado Friday Night

“They are certainly one of the most fearsome (prison gangs). They’re aggressive and they’re violent,” U.S. Attorney Trent Shores said Thursday. “They are absolutely one of the most threatening and one of the most dangerous (gangs).”

The indictment comes after similar charges were filed last week against 54 alleged members of the New Aryan Empire, a white supremacist gang in western Arkansas, but the two are not related, Shores told The Associated Press in a telephone interview following a news conference in Tulsa.

“There is no direct connection alleged in our indictment to the western Arkansas allegations, but it is the Universal Aryan Brotherhood, it is a prison based gang,” that has been affiliated with prison gangs in other states Shores said.

The UAB was formed within the Oklahoma Department of Corrections prison system in 1993, according to the indictment.

“I don’t know how they got here to Oklahoma, but the UAB has patterned itself based upon the Aryan Brotherhood prison gang from California,” said assistant U.S. Attorney General Dennis Fries, the lead prosecutor in the case.

READ MORE: 'I'm Afraid We're Going To See A Surge Of Violence' Says Texas Criminologist Following Recent Mass Shootings

The indictment alleges the 18 indicted and 36 unindicted co-conspirators trafficked methamphetamine and marijuana, assaulted and kidnapped people to intimidate them, and killed rivals and at least one person during an attempted carjacking in Tulsa.

Four of the defendants, Randy Seaton, Richard Young, Michael Clinton and Brandy Simmons were arraigned Wednesday and each pleaded not guilty.

Although the indictment, filed under federal racketeering law, alleges at least six homicides, no murder charges are included.

“We incorporate the murders, the kidnappings, the carjackings and other violent acts into the criminal enterprise as a whole,” according to Shores. “We’re targeting the organization, not just the individual acts.”

Other agencies involved in the investigation include the Tulsa County Sheriff’s Office, the Internal Revenue Service and the U.S. Immigration and Custom’s Enforcement’s Homeland Security Investigations in Dallas.

Homeland Security is involved because “a lot of the methamphetamine that was being transported into Oklahoma came from across the border with Mexico,” Shores said.

MORE NEWS: Texas Grand Jury To Consider Charges In Shooting Death Of Protester Garrett Foster Last Summer

(© Copyright 2019 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)