Virgil Griffith, 39, was sentenced earlier this month to 63 months in jail for advising Pyongyang on how to create cryptocurrency services and blockchain technology to evade the sanctions.

Federal prosecutors say Spaniard Alejandro Cao de Benos, founder of a pro-North Korean affinity organization, and Briton Christopher Emms, a cryptocurrency businessman, recruited Griffith to provide the services.

Both defendants are at large, the US Attorney's Office for the Southern District of New York said in a statement.

The prosecutors accuse Cao de Benos and Emms of arranging for Griffith to travel to North Korea in April 2019 to the Pyongyang Blockchain and Cryptocurrency Conference that they had organized.

At the conference, Emms and Griffith "provided instruction on how the DPRK could use blockchain and cryptocurrency technology to launder money and evade sanctions," the prosecutors alleged.

In the audience were "individuals whom they understood worked for the North Korean government," the statement added.

The instruction was "all for the purpose of evading US sanctions meant to stop North Korea's hostile nuclear ambitions," added Damian Williams, the US attorney in Manhattan.

The accused later allegedly worked to conceal their activity.

The United States prohibits the export of goods, services or technology to North Korea without special permission from the Treasury Department's Office of Foreign Assets Control.

Cao de Benos, 47, and Emms, 30, are charged with one count of conspiring to violate and evade US sanctions, which carries a maximum sentence of 20 years in prison.

Griffith, who holds a doctorate from the California Institute of Technology, pleaded guilty to get a reduced sentence.