U.S. officials say a CIA report says intelligence officials threatened terrorist suspects with guns and in at least one case, with a power drill to try to get them to talk.

Monday, a long-secret report by the CIA's internal investigator will be released, making public the details of the CIA's controversial interrogation techniques during former President George W. Bush's administration.

Sources who have seen the report say CIA interrogators brandished a gun at one prisoner, Abd al Rahim al-Nashiri, the man accused of masterminding an attack on the USS Cole.

They also held a power drill near his body, turning it on and off.

In another case, a gunshot was fired in a room next door, to make one suspect believe another detainee had been executed.

According to U.S. law, threatening a prisoner with "imminent death" is torture and illegal.

Sources who have seen the report say it suggests that the harsh techniques did not lead to useful information.

A spokesman for the CIA said the report has been scrutinized by the U.S. Justice Department, who decided "when and if to pursue prosecution." He added, "that's how the system is supposed to work."

The investigation was completed in 2004, but it has been kept secret. The American Civil Liberties Union fought for the results to be made public.