Polish prosecutors dealing with the allegations that CIA operated a secret prison for terror suspects in Poland pledge a probe into a report that the spy agency paid $15 million in cash to open the black site.

Human rights activists and lawyers accuse Warsaw of striking a secret deal with Washington, under which the CIA allegedly took over an intelligence training academy and used it to secretly detain prisoners as part of the War on Terror. The suspected site is one of dozens allegedly hosted by countries, including Bulgaria, the Czech Republic, Lithuania and Romania.

Polish authorities have been investigating the allegations since 2008.

On Thursday, the Washington Post reported that CIA paid $15 million to Polish intelligence in 2003 for use of the site, handing over the cash flown from Germany via diplomatic pouch. The money was hauled in two cardboard boxes and delivered to Colonel Andrzej Derlatka, deputy chief of the intelligence service, the report said citing former CIA agents.

The newspaper report may contain evidence relating to the Polish investigation, Piotr Kosmaty, spokesman for prosecutors in the Polish city of Krakow, who are dealing with the black site case, said Friday.

"In the course of the investigation that is underway, we will analyze this Washington Post article and will include it in our investigation," Kosmaty told Reuters.

The CIA program involving extrajudicial arrests and detention of terrorism suspects was launched after the 9/11 attacks, according to numerous media reports. Human rights activists allege that prisoners of the secret black sites were subjected to torture there.

Polish authorities deny that their country ever hosted a CIA black site. Foreign Minister Radoslaw Sikorski on Friday declined to comment on the report, calling it "speculation."

Other accounts cited by the newspaper include an episode, in which two interrogators were pulled out of Poland after it was revealed that they had staged a mock execution of a prisoner.

It also cited former CIA officials saying that Khalid Sheikh Mohammed, accused of masterminding the September 11, 2001, attacks, was subjected to waterboarding at the Polish facility.