More than 300,000 computers in dozens of countries are said to have been affected by the attack earlier this year
US officials have publicly blamed North Korea for the devastating 'WannaCry' cyberattack that affected hundreds of thousands of computers around the world earlier this year.
A number of computer security organisations have previously blamed North Korea for the 'ransomware' attack, which encrypted users' important files and demanded a Bitcoin payment in order to have the documents restored.
The attack - which began on May 12th and spread quickly to computers in dozens of different countries - took advantage of a security exploit in Microsoft Windows, and is estimated to have affected more than 300,000 computers.
Hospitals and major businesses were among those hit by the encryption programme before a security researcher from the UK, Marcus Hutchins, managed to halt the attack by activating a so-called 'kill switch'.
Microsoft also issued patches - including to some no longer officially supported operating systems - to help plug the security loophole.
In an article published in the Wall Street Journal, Donald Trump's homeland security adviser Tom Bossert now claims North Korea was 'directly responsible' for an attack that 'cost billions'.
He writes: "We do not make this allegation lightly. It is based on evidence.
"We are not alone with our findings, either. Other governments and private companies agree. The United Kingdom attributes the attack to North Korea, and Microsoft traced the attack to cyber affiliates of the North Korean government."
He added: "North Korea has acted especially badly, largely unchecked, for more than a decade, and its malicious behavior is growing more egregious."
It was not immediately clear if any action was being taken by US authorities against North Korea following the findings.
Media outlets such as BBC reported that the White House was expected to issue an official statement blaming North Korea later today.