Washington ? The CIA spent at least $1 million on the secret intelligence program that aimed to develop hit squads to kill al-Qaida leaders but never went beyond the planning stage, a congressional official said Tuesday.

The highly classified program, which never became operational but remained in existence until it was shut down by CIA Director Leon Panetta in June, is expected to trigger a congressional investigation, other officials said.

The House Intelligence Committee asked the CIA to provide documents about the now-canceled program to kill al-Qaida leaders, and agency officials said it would comply with the request, congressional officials said Tuesday.

According to one official, the agency spent at least $1 million over the eight years that the CIA considered launching the hit teams. The official would not detail the exact amount or its uses. The official and others spoke on condition of anonymity because they were not authorized to discuss the matter publicly.

The House request for documents is likely a precursor to what would likely become a full-blown investigation into the secret operation and why the program was not disclosed to Congress. Panetta, meanwhile, has ordered a thorough internal review of the program, agency spokesman George Little said.

The House Intelligence Committee will try to establish how much was spent on the effort, whether any training was conducted and whether any officials traveled in association with the program, a committee official said. Those factors would determine whether the program had progressed enough to warrant congressional notification, the official said.

House Intelligence Committee Chairman Silvestre Reyes, D-Texas, is expected to decide as early as this week whether to press ahead with a full investigation into the CIA operation.

Panetta told Congress on June 24 that he had canceled the effort to kill al-Qaida leaders with hit teams soon after learning about the operation. Panetta also told lawmakers that former Vice President Dick Cheney directed the CIA not to inform Congress of the specifics of the secret program.

President George W. Bush authorized the killing of al-Qaida leaders in 2001. Congress was aware of that notification.

A congressional official said the secret CIA program was meant to carry out ground attacks with hit teams. Most attempts to kill al-Qaida’s leaders, believed to be hiding in Pakistan’s troubled western border region, have used armed drone aircraft because it is difficult terrain controlled by sometimes hostile tribes. But those strikes have sometimes killed and injured innocent civilians and caused outrage in Pakistan.