The ruling by the European Court of Human Rights marked the first time any court has passed judgement on the so-called "renditions program" that President George W Bush launched after the terror attacks of Sept 11, 2001.
The court, based in Strasbourg, France, said Poland violated the European Convention on Human Rights by failing to stop the "torture and inhuman or degrading treatment" of Abd al-Rahim al-Nashiri and Abu Zubaydah, who were transported to Poland in 2002.
Poland's Foreign Ministry said it could not immediately comment because its legal experts still needed to examine the more than 400-page ruling. It also said it had not yet decided whether to appeal the ruling to the Grand Chamber of the Court.
But President Bronislaw Komorowski called the judgement "embarrassing" to Poland, and damaging both financially and to its image.
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It argued, however, that Poland should have ensured that individuals held in its jurisdiction would not be subjected to degrading treatment. "For all practical purposes, Poland had facilitated the whole process, had created the conditions for it to happen and had made no attempt to prevent it from occurring," the court said.
Foreign Ministry spokesman Marcin Wojciechowski said the ruling was premature and that Poland should have been given the chance to make its own ruling first.
However, the human rights lawyers who brought the case to Strasbourg did so "after it became clear that Polish domestic investigations were turning into a cover-up," said Reprieve, a UK-based legal group that represented Zubaydah in the case.
The lawyers for both suspects hailed the ruling.