The FBI is investigating allegations of civil rights abuses by deputies at Los Angeles County's sprawling jail network, authorities said Monday.
The probe follows complaints by the American Civil Liberties Union of Southern California, which earlier this year said one of its jail monitors saw deputies beat an inmate unconscious.
The scope of the probe was not immediately clear, but sheriff's spokesman Steve Whitmore said FBI agents had apparently helped smuggle a cellphone into one facility so the prisoner could communicate with authorities on the outside.
"The FBI, in collusion with an inmate, snuck a phone into our jail," Whitmore said. "That is a serious breach of our security."
Whitmore said the federal investigation was not warranted because several independent agencies already keep a close eye on LA's jails, which have long drawn criticism for their poor conditions, with prisoners complaining of dead rats in cells and overflowing toilets.
FBI spokeswoman Laura Eimiller declined to comment on the investigation but said federal agents were investigating allegations of civil rights abuses in at least two separate cases.
The investigation was first reported by the Los Angeles Times.
ACLU legal director Peter Eliasberg said conditions at the central jail downtown are dire, with inmates cramped into dorms at double the capacity the rooms were designed for.
To make matters worse, the state is next week due to change how it sentences some criminals, which will send thousands of extra inmates into county custody.
Los Angeles has the nation's largest jail network, with about 15,000 inmates.