The 18-page Presidential Policy Directive 20, issued in October last year but never published, states that what it calls Offensive Cyber Effects Operations (OCEO) “can offer unique and unconventional capabilities to advance US national objectives around the world with little or no warning to the adversary or target and with potential effects ranging from subtle to severely damaging”.

It says the government will “identify potential targets of national importance where OCEO can offer a favorable balance of effectiveness and risk as compared with other instruments of national power”.

The directive also contemplates the possible use of cyber actions inside the US, though it specifies that no such domestic operations can be conducted without the prior order of the president, except in cases of emergency.

The aim of the document was “to put in place tools and a framework to enable government to make decisions” on cyber actions, a senior administration official told the Guardian.