The National Security Committee of the parliament said the prison could house up to eight high-level members of al-Qaida, ABC News reported. The report said a Vilnius guesthouse was converted to a single-cell prison, although that one might not have been used.
The committee began its investigation after ABC News reported in August that Lithuania, Poland and Romania all hosted secret CIA prisons. The report said Lithuanian officials were kept in the dark about the black sites by the CIA and a small group of Lithuanian intelligence agents, the BBC said.
Prime Minister Andrius Kubilius accused the United States of manipulating Lithuanian intelligence agents using "essentially Soviet methods."
ABC said President George W. Bush promised to support Lithuania's admission to NATO.
"The new members of NATO were so grateful for the U.S. role in getting them into that organization that they would do anything the U.S. asked for during that period," said Richard Clarke, the former White House counter-terrorism czar and now an ABC news consultant.