Last month, the CIA had acknowledged that it destroyed videos of officers using allegedly tough interrogation methods while questioning two "terror" suspects.
The acknowledgment resulted in a congressional inquiry and a preliminary investigation by the department.
The interrogations, which took place in 2002, were believed to have included waterboarding, a form of simulated drowning condemned internationally as torture.
"The CIA will of course cooperate fully with this investigation as it has with the others into this matter," Mark Mansfield, the intelligence agency's spokesman said.
Congressional investigators have begun reviewing CIA documents at the agency's headquarters.
The house intelligence committee of the US house of representatives ordered Jose Rodriguez, the former CIA official who directed the tapes be destroyed, to appear at a hearing on January 16.
George Bush, the US president, has denied claims of torture, but has declined to be specific about interrogation methods.