(CNN) -- Twelve current and former Los Angeles County Sheriff's Department deputies were arrested Monday as part of an FBI investigation into alleged misconduct at county jails, a law enforcement source close to the investigation said.
They are expected to make initial appearances in federal court.
The two-year FBI probe focused on allegations that sheriff's officials had fostered a culture in which deputies were permitted to beat and humiliate inmates and cover up misconduct at the nation's largest county jail.
Nine sheriff's officials face indictment charges, and three brothers are charged with criminal complaints, according to court documents.
Criminal corruption and civil rights charges will be announced against "current and former officers of a local law enforcement agency" during an afternoon news conference, according to a press release from the U.S. Attorney's Office for the Central District of California.
The news conference is scheduled to begin at 1 p.m. (4 p.m. ET).
A spokesman for the sheriff's department declined to comment on the allegations.
Last year, a blue-ribbon commission criticized Los Angeles County Sheriff Lee Baca for tolerating a pattern of excessive force by his deputies in the county jails.
The Citizen's Commission on Jail Violence -- composed of several retired judges, a police chief, a religious leader and a civil rights leader, all appointed by the county Board of Supervisors -- issued 77 findings and 60 recommended reforms on the management, oversight and use of force in county jails.
According to the 194-page report, Baca neglected to listen to repeated warnings from the department's civilian watchdogs and inmates-rights advocates about conditions in the jail.
Among the recommendations, the panel recommended harsher penalties for excessive force and dishonesty, and the formation of a new civilian watchdog. The report also criticized the sheriff for not disciplining senior managers who failed to address the jail problems.
The commission based its report on interviews with current and former sheriff's officials, jailhouse witnesses, testimony from experts and internal department records.
The commission called for the creation of an Office of Inspector General that would report to the Los Angeles Board of Supervisors and provide independent oversight of the sheriff's department -- conducting its own investigations, monitoring jail conditions and reviewing the department's audits and inspections.
In a statement last year, Baca said he supported the recommendations.