Khan, who attended high school in Baltimore, was held for more than three years at secret CIA prisons and "subjected to an aggressive CIA detention and interrogation program notable for its elaborate planning and ruthless application of torture, " his lawyers have said, according to court documents.

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The South China Morning Post newspaper, citing sources, said that Mr Li was put under "a disciplinary measure which allows for the detention and interrogation of party members suspected of corruption and other offenses".

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But, given her admission that detainees have been transported to third countries for interrogation, the presumption must be that undisclosed detention centres do exist or have done in the past where such interrogations take place.

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