According to the Telegraph, an attack, which is expected in the next fortnight, is in retaliation for the SolarWinds hack, the large-scale infiltration of American government agencies and corporations discovered late last year that was traced back to the Kremlin.

The US will not target civilian structures or networks, but the hack is instead designed as a direct challenge to Tsar Putin and his cyber army.

The White House confirmed it will take "a mix of actions" — both "seen and unseen" — although it did not provide specifics on when and how it would do so.

US National Security Adviser Jake Sullivan said: "I actually believe that a set of measures that are understood by the Russians, but may not be visible to the broader world, are actually likely to be the most effective measures in terms of clarifying what the United States believes are in bounds and out of bounds, and what we are prepared to do in response."

Sullivan stressed that traditional sanctions alone do not sufficiently raise the cost to force powers like Russia, or China.