Two hacker groups associated with North Korea, the Lazarus Group and APT38, were responsible for the theft last June of $100 million from U.S. crypto firm Harmony's Horizon bridge, the Federal Bureau of Investigation said on Monday.

On Jan. 13, the groups used a privacy protocol called Railgun to launder over $60 million worth of ethereum stolen during the theft in June, the FBI said in a statement

A portion of the stolen ethereum was subsequently sent to several virtual asset providers and converted to bitcoin, the FBI said.

The FBI said North Korea's theft and laundering of virtual currency is used to support its ballistic missile and Weapons of Mass Destruction programs.

In June last year, California-based Harmony said that a heist had hit its Horizon bridge, which was the underlying software used by digital tokens such as bitcoin and ether for transferring crypto between different blockchains.

Reuters in June reported that North Korean hackers were most likely behind the attack on Harmony, citing three digital investigative firms.

Harmony develops blockchains for decentralized finance - peer-to-peer sites that offer loans and other services without traditional gatekeepers such as banks - and non-fungible tokens.

(Reporting by Sneha Bhowmik in Bengaluru; Editing by Leslie Adler)