NEW YORK - Federal prosecutors sued New York City on Thursday over its handling of violence against young inmates held on Rikers Island, calling the jail complex a place where adolescents are "subjected to unconstitutional conditions and confinement."

Preet Bharara, U.S. attorney for the Southern District of New York, said in a filing Thursday that his office wanted to speed reforms at the facility following a Justice Department report in August that found "Rikers is a dangerous place" where a "pervasive climate of fear exists."

At a news conference announcing the suit, Bharara said, "Today we have taken a legal step that we believe is necessary. . . . Much, much more needs to be done," to safeguard inmates at Rikers.

Before federal officials filed the court documents, they notified New York Mayor Bill de Blasio of their intention. Bharara said the mayor supported the move.

Rikers is New York City's main jail complex, housing juveniles, men, and women in separate wards.

"For years, staff responsible for managing [inmates] have had minimal corrections experience, failed to interact with inmates in a professional manner, and failed to adequately monitor inmate conduct," Bharara wrote in the court filings.

He added that the New York City Department of Correction has failed to ensure basic levels of staff professionalism.

"Staff have frequently insulted, humiliated, and antagonized [inmates], often using obscenities and abusive language without fear of any reprimand from supervisors. Such unprofessional conduct provokes physical altercations and leads to unnecessary violence," the court filing said.

Bharara said young inmates suffered "high rates of serious injuries" on a daily basis at the hand of guards and in altercations with one another. Adolescents suffer a disproportionate number of the reported head injuries on Rikers, he wrote in the court filings. For example, he said, from June 2012 through early July 2013, adolescents suffered a total of 239 head injuries, and were twice as likely to suffer such injuries as was the adult population.

Vanita Gupta, the acting assistant U.S. attorney general for civil rights, called the situation at Rikers "deeply disturbing."