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 disclosure would undermine operations against AQAP, as well as potentially damage counter-terrorism collaboration with Saudi Arabia.

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.

‘High-value targets’

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, according to the New York Times.

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 “given the mission of hunting and killing ‘high-value targets’ in Yemen” – the leaders of AQAP who government lawyers had determined posed a direct threat to the US – the officials added.

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 Barak Obama’s counter-terrorism adviser, John Brennan, a former CIA station chief in Saudi Arabia, played a key role in negotiations with the government in Riyadh over building the drone base.

Saudi Arabia is home to some of Islam’s holiest sites and the deployment of US forces there was seen as a historic betrayal by many Islamists, notably the late leader of al-Qaeda, Osama Bin Laden.

It was one of the main reasons given by the Saudi-born militant to justify violence against the US and its allies.

Leaked memo

The revelation of the drone base came shortly after the leaking of a US justice department memo detailing the Obama administration’s case for killing Americans abroad who are accused of being a “senior, operational leader” of al-Qaeda or its allies.

Lethal force is lawful if they are deemed to pose an “imminent threat” and their capture is not feasible, the memo says. The threat does not have to be based on intelligence about a specific attack, since such actions are being “continually” planned by al-Qaeda, it adds.

NBC News said it was given to members of the US Senate intelligence and judiciary committees as a summary of a classified memo on the targeted killings of US citizens prepared by the justice department.

The latter memo was written before the drone strike that killed Awlaki.

Under President Obama, the US has expanded its use of drones to kill hundreds of al-Qaeda suspects in Pakistan, Afghanistan and Yemen. It says it is acting in self-defence in accordance with international law.

Critics argue the drone strikes amount to execution without trial and cause many civilian casualties.

Senators are expected to ask Mr Brennan about drone strikes, the memo and the killing of Awlaki on Thursday when he faces a confirmation hearing on his nomination to become the new CIA director.

BBC