The city has ended Rikers Island's use of solitary confinement for adolescents, and all 16- and 17-year-old inmates have been moved to transitional units as part of efforts to fix a "dehumanizing environment" at the trouble-plagued correctional complex, Mayor Bill de Blasio announced Thursday.

The teenagers will instead receive support and therapy, and may be eligible for "second-chance housing," de Blasio said after a tour of two facilities on the island.

"We know the history. It is a very troubling history. It became a less and less safe environment," he said at a news conference in the chapel of the Robert N. Davoren Complex, where many young detainees reside. "We know it's our mission to find a way to turn people's lives around."

There were 91 adolescents in punitive segregation on Jan. 1, and none as of Dec. 4, city officials said.

An investigative report released in August by U.S. Attorney Preet Bharara revealed a "culture of violence" against young detainees at Rikers and accused correctional officers of relying too excessively on solitary confinement as a punitive tactic. Bharara has threatened a lawsuit to force reforms.

Representatives of Bharara's office visited Rikers two or three weeks ago, and the city is still in "negotiations" with the prosecutor about changes, Correction Commissioner Joseph Ponte said.

A U.S. attorney's office spokeswoman declined to comment on de Blasio's visit and the status of discussions with the city.

The alternative to solitary confinement of troublesome inmates is now to "manage their behavior without using punishment," Ponte said. Guards may separate inmates briefly and talk with them to calm them or assess their mental state before returning them to their group, he said.

De Blasio said he met a 17-year-old who had spent 110 days in punitive segregation with 166 more days scheduled. The teen was moved instead to second-chance housing.

"If he wants to turn his life around, this is the chance to do it," de Blasio said. "He has to move away from violence. He has to work with others."

Young inmates who de Blasio met told him that transitional units help them to learn self-control and included benefits such as more phone time with loved ones.

Other reforms under Ponte, who was appointed in April, include mental health programs and observation and treatment units, the mayor said.

A Manhattan jury convicted a former Rikers captain on the federal charge of deliberately ignoring the medical needs of a mentally ill inmate who swallowed a fatal dose of corrosive detergent. Bharara said, "The convictions of individual wrongdoers at Rikers Island -- as well as the systemic, institution-wide reforms we are pursuing -- should help prevent" future such tragedies.