State governments should abolish the use of solitary confinement for offenders under 18, whether as a punitive or protective measure, two of America's leading advocates for prisoners' rights said in report Wednesday.

Human Rights Watch and the American Civil Liberties Union said brief periods of isolation may be needed as a security measure. However, they contend that longer spans of solitary confinement can cause serious psychological and physical harm to young people, including heightened risk of suicide.

Solitary confinement of adults also can be harmful, the report said. "But the potential damage to young people, who do not have the maturity of an adult and are at a particularly vulnerable, formative stage of life, is much greater."

The report, "Growing Up Locked Down," said lack of detailed state data made it impossible to estimate the number of juveniles subjected to solitary confinement and other forms of isolation at any given time. But it described the practice as widespread, notably among juveniles held in adult facilities.

The report cited psychiatric studies and medical experts warning of the risks that solitary confinement could pose to juveniles. It included input from 49 people who spent time in jails or prisons as minors and described spending at least a month in solitary before turning 18.

"The only thing left to do is go crazy - just sit and talk to the walls," a youth confined in Florida was quoted as saying. "Screaming, throwing stuff around - I feel like I am alone, like no one cares about me. Sometimes I feel like, why am I even living?"

The report's author, human rights researcher Ian Kysel, acknowledged that young people can present serious challenges for corrections officials - both as potential rule-breakers and as potential victims of older inmates.

"Officials may need to use limited periods of segregation and isolation to protect young people from other inmates or even from themselves," he said. "But the extremely stark conditions of solitary confinement that we found across the country, isolation for 22-24 hours a day, often for weeks or months, harm young people in ways that are different than if they were adults."

His report says youths shouldn't be serving time in adult jails and prisons, and instead should be at juvenile facilities where staff trained to deal with young people could find alternative ways to address disciplinary and security problems.

"Punitive schemes can be reorganized to stress immediate and proportionate interventions and to strictly limit and regulate any short-term isolation as a rare exception," the report says.

For now, however, many state and local corrections agencies do house some juveniles in adult facilities, and options for dealing with problems may be limited by lack of space and resources.

Martin Horn, executive director of New York State Sentencing Commission and formerly the top corrections official in New York City and in Pennsylvania, said he opposed any sort of "throw them in the hole" policies that involve rigid isolation and sensory deprivation.

"But we have to be very careful not to deprive officials of necessary tools," he said. "There are and always will be predatory individuals in custody, including youngsters, who can prey on other youngsters. Sometimes physical separation may be the only resort."

He said any decision to isolate a minor in custody should entail extra efforts to "keep them connected to the world, to their family, to social and intellectual stimulation."

According to the new report, New York City was among the jurisdictions making extensive use of punitive segregation for juveniles held at its Rikers Island jail complex.

On Wednesday, Corrections Commissioner Dora Schriro said her department was adopting a new strategy of short-term "time outs" - also known as temporary cell restriction - that should dramatically decrease the use of solitary confinement.

The report by Kysel is the latest in a series of appeals for a halt to solitary confinement of minors.

Last year, the United Nations' investigator on torture, Juan Mendez, urged a complete ban on the practice. The American Academy of Child and Adolescent Psychiatry endorsed that position in April, and said any youth confined in isolation for more than 24 hours should be evaluated by a mental health professional.

Several states have been grappling with controversies and lawsuits related to solitary confinement of juveniles. Earlier this year, Mississippi authorities settled a 2010 lawsuit filed by the ACLU and the Southern Poverty Law Center with an agreement to stop placing minors in solitary confinement for more than 20 hours at a time.