One allegation is that the US maintains secret prisons on European soil.

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Correspondents say he is unwilling to grant US soldiers immunity from prosecution and is unhappy that Afghans are still being held in US-run military prisons on Afghan soil.

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In the US, criminals are punished in prisons for more serious crimes and in jails for lesser offences.

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Meanwhile, Germany's Foreign Minister Frank-Walter Steinmeier is expected to raise the issue of "secret" prisons in talks with US Secretary of State Condoleezza Rice in Washington on Tuesday.

BBC: EU warned on 'secret CIA jails'

He was led away from the courtroom by US Marshals and turned over to the custody of the Federal Bureau of Prisons.

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The UK Foreign Office has confirmed that Britain will be writing to the US, on behalf the EU, to clarify the reports of secret prisons, which were reportedly set up after the 11 September 2001 attacks.

BBC: EU warned on 'secret CIA jails'

"The minister told us that the Ministry of Justice is negotiating with the Treasury for monies to replace prisons in order to bring the cost of the prison estate down, " he added.

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