The United States' use of drones is counter-productive, less effective than the White House claims, and is "encouraging a new arms race that will empower current and future rivals and lay the foundations for an international system that is increasingly violent", according to a study by one of President Obama's former security advisers.
Michael Boyle, who was on Obama's counter-terrorism group in the run-up to his election in 2008, said the US administration's growing reliance on drone technology was having "adverse strategic effects that have not been properly weighed against the tactical gains associated with killing terrorists".
Civilian casualties were likely to be far higher than had been acknowledged, he said.
In an article for the Chatham House journal International Affairs, Boyle said the conventional wisdom over the use of unmanned aerial vehicles (UAVs) needed to be challenged.
He said there was an urgent need for greater transparency because most Americans remained "unaware of the scale of the drone programme ... and the destruction it has caused in their name".
US use of drones has soared during Obama's time in office, with the White House authorising attacks in at least four countries: Afghanistan, Pakistan, Yemen and Somalia. It is estimated that the CIA and the US military have undertaken more than 300 drone strikes and killed about 2,500 people.
Administration officials have argued their use is lawful, though the Pentagon's most senior lawyer, Jeh Johnson, recently admitted that the US was heading for a "tipping point", beyond which it should no longer pursue terrorists by military means because the organisation that Congress authorised the military to pursue in 2001 had in effect been destroyed.
In his study, Boyle said Obama pledged to end the "war on terror" and to restore respect for the rule of law in US counter-terrorism policies.
"Instead, he has been just as ruthless and indifferent to the rule of law as his predecessor ... while President Bush issued a call to arms to defend 'civilisation' against the threat of terrorism, President Obama has waged his war on terror in the shadows, using drone strikes, special operations and sophisticated surveillance to fight a brutal covert war against al-Qaida and other Islamist networks."
Boyle, who teaches at La Salle University, Philadelphia, said the government claim that drones were an effective tool that minimised civilian casualties was "based on a highly selective and partial reading of the evidence".
He argues one of the reasons why the US has been "so successful in spinning the number of civilian casualties" is that it has reportedly adopted a controversial method for counting them: all military-age men in a strike zone are classed as militants unless clear evidence emerges to the contrary.
"The result of the 'guilt by association' approach has been a gradual loosening of the standards by which the US selects targets for drone strikes," his study says.
"The consequences can be seen in the targeting of mosques or funeral processions that kill non-combatants and tear at the social fabric of the regions where they occur. No one really knows the number of deaths caused by drones in these distant, sometimes ungoverned, lands."
Boyle questions the claim that drone strikes have been effective in killing so-called high-value targets, saying records suggested lower-ranked foot soldiers were the ones who had been hit in greatest numbers.
And he also said the strikes had a debilitating effect on local populations and their governments.
"Despite the fact that drone strikes are often employed against local enemies of the governments in Pakistan and Yemen, they serve as powerful signals of the regimes' helplessness and subservience to the United States and undermine the claim that these governments can be credible competitors for the loyalties of the population," he writes.
"The vast increase in the number of deaths of low-ranking operatives has deepened political resistance to the US programme in Pakistan, Yemen and other countries."
Last week, a judge in New York rejected an attempt by the New York Timesto force the US government to disclose more information about its targeted killing of people that it believes have ties to terrorism, including American citizens.
She said the government was not obliged to turn over materials the Times had sought under the federal Freedom of Information Act, even though it had such materials in its possession.
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