LOS ANGELES (AP) — Federal officials say 18 current and former Los Angeles County sheriff's deputies saw themselves as being "above the law," engaging in corruption and civil rights abuses that included beating inmates and visitors, falsifying reports and trying to block an FBI probe of the nation's largest jail system.

The charges were announced at a news conference on Monday after 16 of 18 defendants were arrested earlier in the day. At least two are no longer working for the department and some of those charged are scheduled to appear in U.S. District Court Monday.

"These incidents did not take place in a vacuum — in fact, they demonstrated behavior that had become institutionalized. The pattern of activity alleged in the obstruction of justice case shows how some members of the Sheriff's Department considered themselves to be above the law," U.S. Attorney Andre Birotte Jr. said.

Sheriff's Department spokesman Steve Whitmore said Sheriff Lee Baca would comment later Monday afternoon. "We've cooperated fully with the FBI in their investigation and we'll continue to do so," he said.

Four grand jury indictments and a criminal complaint include accusations that deputies plotted to impede the FBI by moving an informant in the jails and attempting to intimidate a lead FBI agent outside her house; that deputies unlawfully detained and used force on visitors to Men's Central Jail, included detaining and handcuffing the Austrian consul general in one example, and in another, grabbing a man by the neck, forcing his head into a refrigerator, then throwing him to the floor and pepper spraying his eyes; and that deputies falsified reports to make arrests seem lawful or in another case, struck, kicked and pepper sprayed an inmate and made false reports to have the inmate charged with and prosecuted for assaulting deputies.

The FBI has been investigating allegations of excessive force and other misconduct at the county's jails since at least 2011.

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Among those charged with conspiracy and obstruction of justice are two lieutenants, one of whom oversaw the department's safe jails program and another who investigated allegations of local crimes committed by sheriff's personnel, two sergeants and three deputies. All seven are accused of trying to prevent the FBI from contacting or interviewing an inmate who was helping federal agents in a corruption and civil rights probe. One of the investigations involved trying to see if a deputy would accept a bribe to provide the inmate with a cell phone, court documents show.

The indictment alleges the inmate was moved to hide him and false entries were made in the sheriff's databases to make it appear as if he had been released.

In an attempt to find out more information about the investigation, one lieutenant and the two sergeants sought a court order to compel the FBI to provide documents, prosecutors said. When a state judge denied the proposed order, the two sergeants allegedly attempted to intimidate one of the lead FBI agents outside her house and falsely told her they were going to seek a warrant for her arrest, the indictment said.

Birotte wouldn't say whether the lieutenant and two sergeants involved in the obstruction of justice probe were directed by their superiors. He also declined to say whether the alleged abuse was fostered by the department's top brass or deputies were beating up inmates on their own accord.

Others charged in the documents unsealed Monday are a deputy who allegedly possessed an assault weapon that was illegally modified and three deputies — all brothers — for an alleged $350,000 mortgage fraud scheme.

Baca, who has been Sheriff since 1998, has acknowledged mistakes to a county commission reviewing reports of brutality, but he has also defended his department and distanced himself personally from the allegations. He said he's made improvements including creating a database to track inmate complaints. Baca has also hired a new head of custody and rearranged his command staff.

Retired sheriff's Cmdr. Bob Olmsted, who is challenging Baca in the 2014 election, said in a statement Monday that as a commander he tried "several times" to notify the sheriff and his command staff about abuses and misconduct at Men's Central Jail, but his "concerns fell on deaf ears."

"I knew I had to act, and as a result, I notified the FBI of the department's culture and acceptance of excessive force, inmate abuse, sheriff's gangs, and corruption," Olmsted said.

The American Civil Liberties Union sued the Sheriff's Department in 2012 claiming the sheriff and his top commanders had condoned violence against inmates. The organization released a report documenting more than 70 cases of misconduct by deputies.

The Citizens' Commission on Jail Violence, in its 2012 report, said a "force first" approach was employed in jails to establish authority over inmates, rather than as a last resort. The investigators concluded that a "code of silence" blocked the Sheriff's Department from detecting or preventing excessive force used against inmates.

The report said deputies have used force against inmates even "when there was no threat at all," and referred to "a culture of aggression among some deputies in the jails."

Last month the county announced the appointment of veteran Los Angeles County prosecutor Max Huntsman to head a new office of inspector general that will oversee the Sheriff's Department.

The county's jails held more than 18,700 inmates as of Monday.

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Associated Press Writer Robert Jablon contributed to this report.