Los Angeles County's longtime sheriff is facing one of the toughest attacks of his 13-year term, after a civil rights group demanded his resignation and claimed he looked the other way while his sprawling jail network became co-opted by violent and corrupt deputies who routinely abuse inmates.

Sheriff Lee Baca, whose deputies oversee about 15,000 inmates in the nation's busiest jail system, said he welcomed the criticism but disputed the claims made Wednesday by the American Civil Liberties Union. He said he had no intention of stepping down.

The ACLU demanded the four-term sheriff's resignation, saying he and his top commanders are willfully indifferent to claims made by inmates and civilian jail visitors that deputies routinely viciously assault inmates.

In one case, an inmate at the downtown Men's Central Jail said deputies accused him of stealing mail then punched him, breaking an eye socket, and marched him naked to a cell occupied by two gang members.

Deputies repeatedly ignored the man's cries for help as the gang members raped him while another inmate flushed his head down a toilet to muffle his screams, the man, who had been jailed for making criminal threats, said in a sworn declaration.