US President Barack Obama has the legal authority to use an unmanned drone strike to kill his own citizens on American soil.
This is the extraordinary admission in a leaked memo from the US attorney-general Eric Holder.
Mr Holder suggested that using a drone to kill an American on home territory would be justified and permissable in "extraordinary circumstances", comparable to the terrorist attacks of 11 September 2001.
But he added that it was "entirely hypothetical" and "unlikely to occur".
Quizzed about the memo in front of a Senate judiciary committee on Wednesday, Mr Holder emphasised that "the government has no intention to carry out any drone strikes in the United States".
But Senator Chuck Grassley, a Republican from Iowa, told him the use of the phrase "extraordinary circumstances" was "extremely concerning".
"It is imperative that we understand the operational boundaries for use of such force," Mr Grassley continued. "American citizens have a right to understand when their life can be taken by their government absent due process."
In his memo, the attorney-general wrote that "it is possible, I suppose, to imagine an extraordinary circumstance in which it would be necessary and appropriate under the constitution and applicable laws of the United States for the president to authorise the military to use lethal force within the territory of the United States."
The Obama administration has been criticised for its policy towards the use of unmanned drones.
The Telegraph reports that drones have killed an estimated 4,700 people in Pakistan, Yemen and Somalia, a quarter of which are estimated to have been civilians.
According to research by the Bureau of Investigative Journalism, drone strikes killed between 474 and 881 civilians – including 176 children – in Pakistan between 2004 and last year.
Last month it was revealed that the CIA has been operating a drone base in Saudi Arabia for more than a year, which it has used to used to attack and kill senior al-Qaeda operatives.
It emerged that the US newspaper The Washington Post had known about the existence of the base for some time, but did not write about it because it was asked not to by the Obama administration.
The only drone strike "intentionally targeting" a US citizen - the 2011 killing of the US-born cleric and senior al-Qaeda member Anwar al-Awlaki - was carried out by aircraft launched from the base in Saudi Arabia.