The US Central Intelligence Agency (CIA) has been using a secret drone airbase in Saudi Arabia for the last two years, according to a BBC report.

The base was established in order to hunt down Al Qaeda members in the Arabian Peninsula (AQAP), and particularly in Yemen.

A drone flown from there was used in September 2011 to kill Anwar al-Awlaki, a US-citizen who was alleged to be AQAP's external operations chief.

US media have known of the base’s existence since then, but have not reported it.

Senior government officials had said they were concerned that disclosure would undermine operations against AQAP, as well as potentially damage counter-terrorism collaboration with Saudi Arabia, said the report.

The US military pulled out virtually all of its troops from Saudi Arabia in 2003, having stationed between 5,000 and 10,000 troops in the Gulf kingdom after the 1991 Gulf war. Only personnel from the United States Military Training Mission (USMTM) officially remain.

The location of the secret drone base was not revealed in the US reports and the Saudi government has not yet commented.

However, construction was ordered after a December 2009 cruise missile strike in Yemen, the New York Times reported.

It was the first strike ordered by the Obama administration, and ended in disaster, with dozens of civilians, including women and children, killed.

US officials told the newspaper that the first time the CIA used the secret facility was to kill Awlaki.

Since then, the CIA has been tasked with killing ‘high-value’ targets in Yemen who belong to the AQAP, and who have been determined, by government counsels, to pose a direct threat to the US.

Three other Americans, including Awlaki's 16-year-old son, have also been killed in US strikes in Yemen, which can reportedly be carried out without the permission of the country's government.

The Washington Post reported that President Barack Obama's counter-terrorism adviser, John Brennan, a former CIA station chief in Saudi Arabia, played a key role in negotiations with the Saudi government over the base.

The news that Saudi Arabia was home to a CIA airbase followed the leak of a US Justice Department memo, which provided legal justification for killing US citizens abroad, like Awlaki, who were deemed to pose ‘a direct’ and ‘imminent’ threat to the US.