Two British citizens who were fighting for Islamic State were killed in an RAF drone strike in Syria carried out without parliamentary approval, David Cameron said

Classified documents, leaked to investigative news website The Intercept, have revealed the inner workings of the secret US drone program in the Middle East and Central Asia.

A source from within the US intelligence community leaked the documents which appear to undermine American claims that drone strikes have been precise.

The files describe in detail how many people are consulted before President Obama signs off on the order.

The whistleblower, who has already been labelled as the new 'Edward Snowden' on social media, said the public has the right to know about the process by which people are placed on 'kill lists' and "ultimately assassinated on orders from the highest echelons of the US government."

Since taking office in 2009, Obama has expanded the drone program, authorising many more strikes than his predecessor, George W Bush.

The source told The Intercept: "This outrageous explosion of watchlisting — of monitoring people and racking and stacking them on lists, assigning them numbers, assigning them ‘baseball cards,’ assigning them death sentences without notice, on a worldwide battlefield — it was, from the very first instance, wrong.”

The leaked papers appear to show that drone strikes were often carried out based on insufficient and unreliable intelligence and when executed, often compromise further gathering of intelligence.

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The documents reveal that during Operation Haymaker in Afghanistan, drone strikes on 35 'targets' killed at least 219 other people. During a five-month stretch of the operation, a 90 per cent of those killed by the drones were not the intended target.

The deaths were recorded as 'EKIA' (enemy killed in action).

"The military is easily capable of adapting to change, but they don’t like to stop anything they feel is making their lives easier, or is to their benefit. And this certainly is, in their eyes, a very quick, clean way of doing things. It’s a very slick, efficient way to conduct the war, without having to have the massive ground invasion mistakes of Iraq and Afghanistan.

"But at this point, they have become so addicted to this machine, to this way of doing business, that it seems like it’s going to become harder and harder to pull them away from it the longer they’re allowed to continue operating in this way."

The documents, slides and analysis were posted on the website on Thursday as 'The Drone Papers'.

International lawyers argue that air strikes using drones are state-sanctioned assassinations where the targeted suspected terrorist has no opportunity to defend the case against them.

Last month David Cameron disclosed that an RAF drone had killed two Britons in an attack near the city of Raqqa, describing it as an "act of self defence".

Reyaad Khan, from Cardiff, the primary target, and Ruhul Amin, from Aberdeen, died on August 21.

Announcing the operation, the Prime Minister said it was "entirely lawful" and confirmed that the Government's senior law officer, Attorney General Jeremy Wright, was consulted and "was clear there would be a clear legal basis for action in international law".

Ministers have resisted calls for the full advice to be published.

The Intercept, run and edited by Glenn Greenwald, Laura Poitras, and Jeremy Scahill. The same journalists who worked with Snowden on his disclosures about US global surveillance by the National Security Agency.

Former NSA contractor Edward Snowden contacted journalist Greenwald in 2012 with 'sensitive documents'. He then contacted film-maker Poitras in 2013 and began working with both of them to disclose the documents on US global surveillance.

The Intercept, created and funded by eBay founder Pierre Omidyar, has not revealed their new source, but at the end of Citizenfour, the documentary about Snowden, Greenwald talks about a new source who is talking to Scahill. Snowden tells Greenwald: ‘That person is incredibly bold’.

The full report on the leaked documents and US drone program can be viewed on the website here.

There’s never been a major leak of documents relating to the U.S. drone program. Until now. https://t.co/IPnqTDv5Ou https://t.co/Opnqg0iqCb — The Intercept (@the_intercept) October 15, 2015

Step by step of how Obama administration kills people by drone explained by @coracurrier https://t.co/blm6CG6q3v pic.twitter.com/b8q5wgAkSq — Nick Turse (@nickturse) October 15, 2015

This is what the terror watchlist looks like at drone operators' terminals: https://t.co/YDC3ddcdW0 pic.twitter.com/EJkPuq4Gir — jeremy scahill (@jeremyscahill) October 15, 2015

Secret drone documents offer look into kind of killing that now defines the War on Terror: https://t.co/IPnqTDv5Ou pic.twitter.com/ab9I9K2h8z — The Intercept (@the_intercept) October 15, 2015

US designated people killed "enemy killed in action" even if they were not intended targets: https://t.co/mpCikkQex1 pic.twitter.com/gPjl6AFqIn — Ryan Gallagher (@rj_gallagher) October 15, 2015

In an astonishing act of civil courage, one American just shattered an unspeakable lie. https://t.co/2H81IMKPha pic.twitter.com/OwIqygfpqJ — Edward Snowden (@Snowden) October 15, 2015

Drones: Unmanned aircraft

The Predator, and its successor, the Reaper, is a remote-controlled aircraft system which first came into use in 1995. It can be deployed for reconnaissance and missile attack. The air-strike version is armed with Hellfire missiles and is known to have been deployed over Afghanistan, Pakistan, Bosnia, Serbia, Iraq, Somalia, Syria and Yemen.

Belfast Telegraph