The disclosure of details about the CIA’s brutal interrogation programme could provide new leads for Polish prosecutors investigating how much Poland’s leaders at the time knew about a secret jail the agency was running in a Polish forest.

Prompted by a US Senate report on the CIA’s ‘black sites’ for interrogating al-Qaeda suspects, former Polish president Aleksander Kwasniewski, at a joint news conference with former prime minister Leszek Miller, said on Wednesday he knew about the facility in Poland.

He said the CIA had denied Polish officials access to the site, a villa on the grounds of a Polish intelligence training academy, so they did not know people inside were being tortured. He said that while he and Miller knew people were detained there, they were told the detainees were cooperating willingly with US intelligence and would be treated as prisoners of war.

Lawyers for former detainees say, however, that even if the detainees were treated as prisoners of war – which the lawyers dispute – it is illegal to detain anyone in secret, and Poland had a legal obligation to prevent this happening.

The report’s publication is giving rise to uncomfortable questions in countries that hosted the ‘black sites’ and may complicate future security cooperation with the US.