The Central Intelligence Agency's Inspector General will conduct what could be the first of several investigations into the CIA drone strikes that killed American and Italian hostages and two US-born Al-Qaeda militants, US government sources said on Friday.
The Senate Intelligence Committee also is reviewing the attacks, a Congressional source said.
Depending upon the results of the CIA watchdog's investigation, US President Barack Obama could establish an outside investigative panel to examine the drone attacks, and broader US drone policy, said a US official, speaking on condition of anonymity.
Obama created a similar panel in August 2013 to examine US electronic surveillance following revelations by former NSA contractor Edward Snowden.
"We're going to review what happened. We're going to identify the lessons that can be learned and any improvements and changes that can be made," Obama said in a speech on Friday marking the 10th anniversary of the Office of the Director of National Intelligence.
The White House has revealed few details about the reviews, declining even to identify the CIA Inspector General as the office doing the initial probe. The CIA's role in drone strikes remains officially classified.
"At this point, I wouldn't even be in a position to promise that we would have an extended public discussion of those reviews, given the sensitive nature of … what they're reviewing," White House Press Secretary Josh Earnest said.
On Thursday, Obama acknowledged that a US "counter-terrorism operation" in January inadvertently killed US hostage Warren Weinstein and an Italian, Giovanni Lo Porto.
US born militant Ahmed Farouq was killed in a drone strike which also resulted in the deaths of the hostages while American militant Adam Gadahn was killed in a separate drone attack.
But the CIA did not know any of those four individuals were present at the compounds at which drone-borne missiles were aimed, the officials said.
Instead, the CIA had concluded, after protracted surveillance of the compounds, that they housed individuals believed to be senior Al-Qaeda operatives and facilitators.
Under secret government procedures, the president is supposed to approve any drone strikes which knowingly target Americans. Other senior officials are empowered to authorize drone attacks on foreigners if there is strong intelligence linking them to terrorism.
When the CIA first started launching lethal drone attacks against suspected militants, it was required to have extremely high confidence that a specific individual was at a specific place at a specific time.
However, President George W. Bush in 2008 authorized "signature strikes," lethal attacks against individuals who fit the profile of militants but whose precise identity is not known.