North Korea was “directly responsible” for a massive cyber attack in May that wreaked havoc on tens of thousands of organisations worldwide from the UK’s National Health Service to US delivery services company FedEx, the White House has alleged.

The US “today publicly attributes the massive ‘WannaCry’ cyberattack to North Korea”, Thomas Bossert, a White House homeland security adviser, wrote in the Wall Street Journal in a move probably aimed at increasing international pressure on the reclusive regime.

The development is also likely to further heighten tensions between Washington and Pyongyang that have threatened to spill over into conflict. US President Donald Trump on Monday vowed to “take care” of the regime’s rapidly advancing nuclear and ballistic missile programmes, which he deemed a threat to “millions of Americans”.