The US Air Force plans to spend $100 million to train airmen on using the aircraft's spy technology over the next two years. -Photo by Reuters

The media also claimed that US officials were citing Pakistan's tacit approval of the drone attacks to justify their decision to continue the air strikes that have killed hundreds of people in the last two years.

The need to justify the attacks followed a UN report last week which warned that using drones had serious legal problems as international laws do not approve such actions.

Since then, several US officials have defended the Obama administration's decision to expand the drone strikes, initiated by their predecessors in the White House.

The most interesting comments came on Saturday from US Secretary of Defence Robert Gates who apparently tried to protect the American military and intelligence agencies from possible legal repercussions.

“CIA and the US military are fully accountable to Congress in all their operations,” said Mr Gates when asked to comment on the UN report. “I have no doubt whatsoever that the intelligence committees in the US Congress are fully informed of the activities the CIA is carrying out,” he told journalists in Singapore.

Diplomatic observers in Washington say that Congress's involvement can provide a legal cover to the controversial air strikes, at least in US courts.

Meanwhile, the Pentagon's technical response to this legal problem is the introduction of a manned aircraft known as the MC-12 Liberty. It is a four-person, twin-engine propeller plane based on a civilian aircraft used around the world.

Drones are operated by the CIA and critics say that intelligence agencies do not observe the legal code that apply to uniformed soldiers. The new plane is operated by US Air Force personnel who follow a legal code, which includes international obligations observed during an armed conflict.

The Pentagon claims that the intelligence gathered by MC-12 crews has led to the capturing of 60 terrorists and criminals in Iraq and the killing or capturing 20 insurgents in Afghanistan, including four commanders.

The MC-12 aircraft also helped locate hundreds of roadside bombs around Marjah in advance of a Marine-led offensive there in March. The first aircraft arrived in Afghanistan last December.

The US Air Force plans to spend $100 million to train airmen on using the aircraft's spy technology over the next two years.

Yet, all indications are that the unmanned drones will remain the weapon of choice, at least for the CIA, in the foreseeable future.

And two CIA officials, Paul Gimigliano and George Little, when asked to comment on the UN report, defended their agency's action.

“Without discussing or confirming any specific action or programme, this agency's operations unfold within a framework of law and close government oversight,” they said.

“The accountability's real, and it would be wrong for anyone to suggest otherwise.”

The White House spokesman declined to comment on the UN report, but pointed to a recent speech by the State Department legal adviser, Harold Koh, that partly outlined the Obama administration's legal rationale.

Mr Koh has invoked America's “armed conflict with Al-Qaeda, the Taliban and associated forces” as a justification for taking out individual fighters and leaders.

Mr Alston made a measured and reasoned legal attack on the general use of targeted killings by governments against non-state actors, but he specifically criticised the American drone campaign, expressing doubt that the US could claim to be in an armed conflict with Al Qaeda and concluding that, “Outside the context of armed conflict, the use of drones for targeted killing is almost never likely to be legal.”