North Korea may have raked in more than $200 million in digital cryptocurrency transactions last year, diluting the impact of stiff international sanctions over its nuclear and missiles programme.

The huge haul of an estimated 11,000 Bitcoins was revealed by Priscilla Moriuchi, a former US National Security Agency officer, in an interview with Radio Free Asia.

If the regime had monetised them when their price peaked in mid-December, it would have made $210 million, although that value had fallen to $120m by January.

Ms Moriuchi, who now works for cyber threat intelligence firm Recorded Future, believes the cryptocurrency was acquired through mining or hacking.

Financial security experts believe North Korea is using virtual coin markets to inject cash into its flagging economy, which is struggling under the weight of severe international sanctions.