Mayor de Blasio announced Monday that the city will end the use of solitary confinement in its jails, agreeing to make a change long advocated by criminal justice reformers.

“We have proven that we can keep jails safe with much less use of solitary confinement punitive segregation. So let’s take the next step, let’s end solitary confinement altogether,” de Blasio said.

Effective immediately, the city will expand the list of underlying medical conditions that make an inmate ineligible for solitary confinement. Until now, the Department of Correction only prohibited inmates who are pregnant or have serious mental illness from being placed in solitary.

The mayor also said a special working group will be named to come up with a plan to eliminate solitary and other forms of punitive segregation altogether.

The reforms come three days after the city disciplined 17 correction officers for the death of Layleen Polanco, the 27-year-old transgender woman who died in solitary confinement last June after a seizure. Until now, the mayor had opposed eliminating solitary confinement, which has been used as a tool to enforce jail discipline.

• 17 Staff Members Disciplined After Investigation Into Layleen Polanco's Death on Rikers

"Layleen Polanco should have not been in Rikers to begin with, Layleen Polanco should have not been in solitary confinement and Lord knows she deserves justice."

The "working group" charged with coming up with a plan for eliminating punitive segregation will have a representative from the Board of Corrections, the Department of Correction and the Correction Officers Benevolent Association as well as a formerly incarcerated individual.

Anisah Sabur, who spent 61 days in solitary confinement at Rikers Island in 1989, has been a member of the #HaltSolitary campaign.

"It inhumane. It is a practice of oppression and control,” Sabur said.

In October, the #HaltSolitary campaign released a plan on how city jails could abolish the practice. Sabur say the city does not need a special panel to study the issue.  

"They don't need a working group. The campaign is their working group. We have been giving them enough information work on and they are not doing it,” Sabur said.

Other advocates are calling on the mayor to end to practice immediately. The working group is expected to present its recommendations to end punitive segregation in the fall.