US attorney general Eric Holder has appointed two investigators to determine the source of a recent spate of leaks to the press: in particular, leaks of details about America's covert military programmes.

Congressional Republicans have accused the Obama administration of intentionally leaking sensitive information to the New York Times, in order to bolster the president's foreign policy credentials just months before the November elections. The White House firmly denies this.

The stories, about cyberwar strategy against Iran and protocols for US drone strikes, reveal key details about the broader powers President Obama has assumed in his aggressive military strategy to kill suspected terrorists and contain Iran.

Read more: Should the US president really have a licence to kill? We probe deeper into this moral minefield.