Updated

New York City jails holding teenage inmates are extremely violent and unsafe -- and major reforms are needed.

That's the blunt conclusion of a 2 1/2-year federal investigation into the three Rikers Island facilities that hold 16- to 18-year-olds. It found the constitutional rights of young inmates are routinely violated, and they are subject to the "rampant use of unnecessary and excessive force" by guards.

Among other findings, the federal lawyers say there is a "deep-seated" culture of violence at Rikers and jail officials too often use solitary confinement, especially for mentally ill inmates.

Mayor Bill de Blasio has vowed to reform the nation's second-largest jail system, with about 11,500 daily inmates.