The Department of Justice today sought court permission to join a civil lawsuit which accuses New York's Department of Correction of using excessive force against the youngest inmates.
The intervention follows a two-and-a-half-year investigation which Manhattan attorney Preet Bharara said uncovered "a pervasive and deep-seated culture of violence" at the jail in the East River.
Rikers Island is one of the largest municipal jails in the United States with an average daily population of 14,000. Most of the inmates are in pre-trial detention.
The violence triggered a staggering number of injuries. For example, in 2013, there were 565 incidents of force against an average of 683 underaged detainees.
New York one of only two states in the US that automatically charges all those aged 16 and over as adults.
US Attorney General Eric Holder said he was taking legal action to ensure that vital reforms, recommended in a report in August, were implemented swiftly.
Holder said there was "alarming evidence" of excessive use of force against juveniles, and a systemic failure to protect them from violence and solitary confinement.
The youngest inmates are subject to "rampant use of unnecessary and excessive force" inflicted by prison staff and other inmates, prosecutors said.
"This violence is the result of widespread and longstanding systemic deficiencies within DOC and its jail complex on Rikers," said Bharara in court papers filed on today.
