North Korean hackers who previously attacked the NHS among others are believed to be behind the world’s largest cryptocurrency heist, worth more than £450million.
The US Treasury Department linked the theft to a digital currency address used by a group dubbed Lazarus.
The hackers stole hundreds of millions of pounds of cryptocurrency from online game Axie Infinity.
Blockchain analytics firms said the designation confirmed that North Korea was behind the break-in.
A Treasury Department spokesperson said: “The United States is aware that the DPRK has increasingly relied on illicit activities – including cybercrime – to generate revenue for its weapons of mass destruction and ballistic missile programs as it tries to evade robust U.S. and U.N. sanctions.”
Lazarus has been in operation for around a decade with the blessing of the North Korean government.
A statement from the FBI said: “The FBI continues to combat malicious cyber activity including the threat posed by the Democratic People's Republic of Korea to the U.S. and our private sector partners.
“Through our investigation we were able to confirm Lazarus Group and APT38, cyber actors associated with the DPRK, are responsible for the theft of $620 million in Ethereum reported on March 29.
“The FBI, in coordination with Treasury and other U.S. government partners, will continue to expose and combat the DPRK’s use of illicit activities – including cybercrime and cryptocurrency theft – to generate revenue for the regime.”
Aleksander Larsen, the co-founder of Sky Mavis, which makes Axie Infinity, declined to comment.
The US says the Lazarus hacking group is controlled by the Reconnaissance General Bureau, North Korea's primary intelligence bureau.
It has been previously accused of involvement in the WannaCry ransomware attacks in 2017 which affected 200,000 computers worldwide, including the NHS.
It is also believed to have been responsible for hacking international banks and customer accounts, and the 2014 cyber-attacks on Sony Pictures Entertainment.
Earlier this year the US Justice Department announced Eun Young Choi as its first director of the National Cryptocurrency Enforcement Team.
She said: “The department has been at the forefront of investigating and prosecuting crimes involving digital currencies since their inception.
“The NCET will play a pivotal role in ensuring that as the technology surrounding digital assets grows and evolves, the department in turn accelerates and expands its efforts to combat their illicit abuse by criminals of all kinds.
“I am excited to lead the NCET’s incredible and talented team of attorneys, and to get to work on this important priority for the department.”
