North Korea has been blamed for WannaCry, the cyber attack that forced hospitals, banks and other companies into meltdown in May.
White House homeland security adviser Tom Bossert said on Tuesday that North Korea has acted “badly” and “unchecked” for more than a decade.
Mr Bossert called WannaCry a “reckless” attack that affected UK healthcare system and “put lives at risk”.
And he hit out at North Korea as he condemned the cyber attack.
He said during a press conference: “Its malicious behaviour is growing more egregious and stopping that malicious behaviour starts with this step of accountability.
“After careful investigation, the United States is publicly attributing the massive cyber attack to North Korea.
“We did not make this allegation lightly. We do so with evidence and we do so with partners.
“The attack was widespread and cost billions, and North Korea is directly responsible.”
Kim Jong-un’s regime has long been suspected of the WannaCry cyber attack which targeted 150 countries and sent many of the UK’s NHS hospitals into meltdown.
In October, the British Government said it “strongly” believed North Korea was responsible for the ransomware attack.
Following the allegation from Theresa May’s security minister Ben Wallace, North Korea opposed the accusation and said it was “despicable” and “an act beyond the limit of our tolerance”.
A statement from the state’s propaganda news agency KCNA slammed the allegation and warned Britain to “seriously reflect” on what was being claimed.
The statement said: “The UK has made another attempt to incriminate the DPRK as a cyber-criminal. The DPRK has clarified our principled stand, on every opportune occasion, to oppose terrorism in all its forms and manifestations.”