Blackwater staff provided security for US officials in Iraq
The CIA hired contractors from the US private security firm Blackwater as part of a secret programme to track and kill top al-Qaeda figures, reports say.
The New York Times quotes current and ex-government officials as saying Blackwater helped the CIA with planning, training and surveillance.
Several million dollars were spent on the programme but no militants were caught or captured, the report says.
Blackwater staff were used to guard US government personnel in Iraq from 2003.
But they were accused of using excessive force on a number of occasions, including the killing of 17 civilians in Baghdad in 2007.
The North Carolina-based firm has not had its licence to operate in Iraq renewed.
The company, which was founded by Erik Prince, has since been re-named Xe.
The New York Times reports that the CIA did not have a formal contract with Blackwater for the programme to locate and kill senior members of al-Qaeda.
Instead, they had individual agreements with top officials in the firm, the paper goes on to say.
It is not clear whether the US spy agency planned to use Blackwater contractors to actually capture and kill the militants, or just help with the training and surveillance of the programme, the report says.
Meanwhile, the Washington Post reports that the assassination programme was initially launched in 2001 as a CIA-led effort to kill or capture top al-Qaeda figures using the agency's paramilitary forces.
But in 2004, after briefly terminating the programme, the CIA decided to revive it using outside contractors, the Post quotes officials as saying.
Leon Panetta - who became director of the CIA under President Obama's administration - is said to have learnt about the secret programme in June.
The next day he called an emergency meeting with congressional intelligence committees to tell them about its existence, and to say that it was being cancelled.
The New York Times quotes officials as saying the fact that the CIA used an outside company for the programme was a major reason Mr Panetta became alarmed and called the meeting.
Although some controversial work, including the interrogation of prisoners, has been outsourced in recent years, the fact that outsiders were used in a programme with "lethal authority" raised concerns about accountability in covert operations, officials were quoted as saying.
The House of Representatives' intelligence committee is investigating whether the CIA broke the law by not informing Congress about the programme for eight years.
Democratic Senator Dianne Feinstein, chairwoman of the Senate intelligence committee, said last month that Mr Panetta told Congress former Vice-President Dick Cheney was behind the secrecy.
But some Republicans accuse the Democrats of trying to make political capital from the situation.
"I think there was a little more drama and intrigue than was warranted," Representative Peter Hoekstra, the most senior Republican on the House intelligence committee, told the Times.