Amnesty International released a report Friday on what it brands as a violation of human rights in Japanese prisons, to coincide with the U.N.-designated "International Day in support of victims of torture."

The human-rights group's report, titled "Japan: Abusive Punishments in Japanese Prisons," says inmates in Japan are subjected to cruelty and humiliation. For example, the report alleges that prisoners are restrained with leather and metal handcuffs and forced to wear slit cut pants in order to defecate without the use of their hands.

The report also cites the problem of "protection cells," which are supposed to be used to confine those who allegedly attempt to escape, act violently or are deemed at risk of committing suicide.

Instead, prison guards use such cells as a means of punishment, keeping prisoners in them for two to three days, the report says. The prisoners are monitored continuously via video cameras and are kept handcuffed throughout the confinement, even during mealtimes, sleeping periods or when using the toilet, according to the report.

Prisoners rarely complain of such abuses because they fear they may not be released on parole, Yuichi Kaido, lawyer and secretary general of the Tokyo-based Center of Prisoners' Rights, told a news conference.

"When they decide to sue, it means they have determined they will spend the rest of their sentence in solitary cells," he said, adding that many give up legal action after being informed of the risks by the center.

Amnesty said these conditions at Japanese prisons are in violation of international human-rights standards and "must not be imposed on prisoners under any circumstances."