WASHINGTON, Jan 25 (Reuters) - U.S. President Barack Obama in an opinion piece published in the Washington Post on Monday announced that he is banning solitary confinement for juveniles in federal prisons, citing concerns about its harmful psychological effects.

The move comes amid a national movement demanding criminal justice reform, which was sparked by numerous high-profile police killings in recent years.

In the opinion piece, Obama also said solitary confinement could no longer be used as a punishment for low-level infractions. He said the package of changes would include an expansion of treatment for mentally ill prisoners and an increase in the amount of time inmates in solitary can spend outside of their cells.

He said the changes would affect some 10,000 federal prisoners and stemmed from a review of the practice he directed the U.S. Justice Department to conduct last summer.

Obama cited the story of Kalief Browder, a black 16-year-old who was arrested in 2010 and spent almost two years in solitary confinement in New York City's Rikers Island jail before his release in 2013 and eventual suicide two years later.

Solitary confinement, Obama wrote, is "increasingly overused on people such as Kalief, with heartbreaking results - which is why my administration is taking steps to address this problem."

Obama said research suggests solitary confinement has been linked to depression, alienation, withdrawal, a reduced ability to interact with others and the potential for violent behavior.

He said states that have worked to cut back their use of the technique have seen drops in assaults on staff and more prisoners engage in rehabilitation programs.

Obama said he hoped the changes he has ordered in the treatment of federal prisoners would serve as a model for reforms by state and local corrections systems.

"There are as many as 100,000 people held in solitary confinement in U.S. prisons - including juveniles and people with mental illnesses," Obama said. "As many as 25,000 inmates are serving months, even years of their sentences alone in a tiny cell, with almost no human contact."

Just last month, New York state agreed to end its "overreliance" on solitary confinement as a means to discipline inmates in its prisons, as part of a settlement to a lawsuit brought against the state by the New York Civil Liberties Union.

California last September also agreed to sharply cut its use of solitary confinement as part of a sweeping settlement to a lawsuit brought by prisoners.

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