The CIA conducts lethal drone attacks against targets in Yemen from a base inside Saudi Arabia, according to the New York Times newspaper, including the attack that killed American-born Anwar al-Awlaki.
The existence of the base has been reported before, but its exact location has been withheld by various news outlets at the request of the Obama administration.
The base was first used in 2011, the Times reported, to launch the drone strike that killed Awlaki, a key ideologue in Al-Qaeda in the Arabian Peninsula (AQAP).
Any operation by US military or intelligence officials inside Saudi Arabia is politically and religiously sensitive. AQAP and other groups have used the kingdom's close relationship with the US to recruit new members, and to stir internal dissent against the Saudi government.
Disclosure of the base's location comes at a time of heightened scrutiny of US drone operations in Pakistan, Yemen, Somalia and elsewhere.
John Brennan, the president's top counterterrorism adviser and a prominent architect of the drone programme, will appear before Congress on Thursday for confirmation hearings. Obama has nominated Brennan to head the Central Intelligence Agency.
He will undoubtedly face questions about a leaked Justice Department memo, first reported by NBC News, which authorises the president to kill American citizens who are "senior leaders" of militant groups, even if they have not been directly involved in attacks against the US.
The White House defended the memo earlier this week.
"We conduct those strikes because they are necessary to mitigate ongoing actual threats, to stop plots, to prevent future attacks and, again, save American lives," Jay Carney, White House spokesman, said.
"These strikes are legal, they are ethical, and they are wise."
Among the most controversial of the attacks were the September 2011 killings in Yemen of Awlaki and Samir Khan, another alleged AQAP member. Both were US citizens who had never been charged with a crime.
"I would point you to the ample judicial precedent for the idea that someone who takes up arms against the United States in a war against the United States is an enemy and therefore could be targeted accordingly," Carney said.
The American Civil Liberties Union (ACLU) called the document is "profoundly disturbing."
"According to the white paper, the government has the authority to carry out targeted killings of US citizens without presenting evidence to a judge before the fact or after, and indeed without even acknowledging to the courts or to the public that the authority has been exercised," Jameel Jaffer, ACLU's deputy legal director, wrote on the organisation's website.
"Without saying so explicitly, the government claims the authority to kill American terrorism suspects in secret."
NBC said the leaked memo was given to the Senate intelligence and judiciary committees in June, on the condition that it be kept confidential and not discussed publicly.