The US Central Intelligence Agency has been operating a secret airbase for unmanned drones in Saudi Arabia for the past two years.
The facility was established to hunt for members of al-Qaeda in the Arabian Peninsula, which is based in Yemen.
A drone flown from there was used in September 2011 to kill Anwar al-Awlaki, a US-born cleric who was alleged to be AQAP's external operations chief.
US media have known of its existence since then, but have not reported it.
Senior government officials had said they were concerned that it’s disclosure would undermine operations against AQAP, as well as potentially damage counter-terrorism collaboration with Saudi Arabia.