The CIA has been hiding and interrogating some of its most important al Qaeda captives at a Soviet-era compound in Eastern Europe, according to U.S. and foreign officials familiar with the arrangement.

The secret facility is part of a covert prison system set up by the CIA nearly four years ago that at various times has included sites in eight countries, including Thailand, Afghanistan and several democracies in Eastern Europe, as well as a small center at the Guantanamo Bay prison in Cuba, according to current and former intelligence officials and diplomats from three continents.

The hidden global internment network is a central element in the CIA’s unconventional war on terrorism. It depends on the cooperation of foreign intelligence services, and on keeping even basic information about the system secret from the public, foreign officials and nearly all members of Congress charged with overseeing the CIA’s covert actions. … the CIA has not even acknowledged the existence of its black sites…