A prosecutor says the U.S. has rejected four requests from Poland for assistance in its investigation into a secret CIA prison.

Piotr Kosmaty, spokesman for prosecutors in Krakow, told The Associated Press Tuesday that in August the U.S. Justice Department refused requests for documents and information. It also refused to question three alleged victims, who claim they were held and treated harshly at a secret CIA prison in Poland between 2001-2003. They are currently held in Guantanamo Bay.

The U.S. authorities argue that granting these requests would be against national security interests.

Another request was previously denied and one more is being debated, Kosmaty said.

Human rights groups, European officials and the U.S. Senate's Intelligence Committee have reported there were CIA "black sites" in Poland, Romania and Lithuania.