The US government's internal guidelines for targeted killings of al-Qaeda suspects allow for such strikes against US citizens abroad, as long as they are believed to be senior leaders of the group and still engaged in operations, a leaked justice department memo shows.

The 16-page document, released by the US-based NBC news service on Tuesday, provides a legal rationale behind the US administration's use of drone strikes against al-Qaeda suspects. The memo says that it is lawful for the US to target al-Qaeda-linked US citizens if they pose an "imminent" threat of violent attack against other US citizens, and that delaying action against such people would create an unacceptably high risk.

Such circumstances may necessitate expanding the concept of "imminent threat", the memo says. "The threat posed by al-Qaeda and its associated forces demands a broader concept of imminence in judging when a person continually planning terror attacks presents an imminent threat," the document says.

Specific imminent threat

The memo said that authorities did not have to possess information regarding a specific imminent attack against the US. It does require that the capture of terrorism suspects be first deemed unfeasible, and that any such lethal operation by the US targeting a person comply with fundamental law-of-war principles.

"A decision maker determining whether an al-Qaeda operational leader presents an imminent threat of violent attack against the United States must take into account that certain members of al-Qaeda [...] are continually plotting attacks against the United States" and that "al-Qaeda would engage in such attacks regularly to the extent it were able to do so", the document says.

The document also says that a decision maker must take into account that "the US government may not be aware of all al-Qaeda plots as they are developing and thus cannot be confident that none is about to occur; and that [...] the nation may have a limited window of opportunity within which to strike in a manner that both has a high likelihood of success and reduces the probability of American casualties".