The U.S. government says it has begun a formal review process of prisoners at Guantanamo Bay as part of renewed effort to close the prison.

Officials will be reviewing the cases of about 45 men who the U.S. previously said were too dangerous to be released. A Pentagon statement Wednesday said the officials will consider whether circumstances have changed.

The U.S. says it can detain prisoner indefinitely at Guantanamo under international law. The U.S. holds 164 men at Guantanamo, including six currently facing trial by military commission for terrorism offenses. Human rights groups have called for all to be released.

President Barack Obama vowed to close the prison upon taking office but Congress imposed restrictions that have brought releases to a virtual halt.

(AP)