US president-elect Barack Obama's review of Guantanamo Bay prisoners must weigh the threats posed by an extraordinarily diverse group, from die-hard jihadists to innocent men swept up in war.

Two presidential transition team advisers said on Monday that Obama is preparing to issue an executive order in his first day or week in office setting in motion the extensive survey needed to close the US military prison in Cuba.

His team faces a daunting task. Some cases are clear cut. Khalid Sheikh Mohammed, brought to Guantanamo in 2006 from CIA custody, has claimed responsibility for the Sept 11 attacks. He said he wants to be executed to achieve martyrdom.