Mayor Bill de Blasio conceded Friday that his administration bungled an effort to separate young inmates on Rikers Island from older prisoners and said it was being put on hold.

“There were unintended consequences here, and we saw particularly — because of gang affiliations — some situations where it appeared to be making the situation less secure and making people less safe,” the mayor said on WNYC radio.

He was responding to questions about an earlier Politico report that the Department of Correction had quietly reversed course on a three-year-old plan to house young adults between 18 and 21 years old at a specially designated jail.

The change was enacted to provide “age-appropriate programming” that would better prepare the young inmates for life after prison.

“We do believe that the ideal is to have separation — but it has to be done in a way that improves safety and doesn’t undermine safety,” Hizzoner said.

“And when the first efforts were made, we found out it was not working as planned. Our plans sometimes have very good intentions, but we have to be open to understanding the unintended consequences,” he continued.

“.. So we are reworking it. We are temporarily allowing the different age groups together because we think it will allow us to secure the situation better for the near term. But then the goal is, as we move into new spaces soon, is to return that notion of having age groups separated again.”

The city is planning to close Rikers and replace it with new borough jails within the next decade.