The group of men who briefly took control of the North Korean embassy in Madrid in February are believed to have made off with vital decryption computers that Pyongyang needs to communicate with its diplomatic missions and agents overseas, according to a former North Korean diplomat.

Thae Yong-ho, who was the deputy head of the North Korean embassy in London until he defected with his family in 2016, said in a post on his website that the “transformation computer” that was apparently taken “is considered more important than human lives”.

The loss of the equipment potentially compromises the unbreakable code that Pyongyang uses to relay its orders overseas, Mr Thae said, and would “critically harm” the regime.

The alleged leader of the attack on the North Korean mission in Madrid on February 22 - Adrian Hong Chang, of Mexican nationality - offered the stolen information to the FBI five days later, a Spanish court said Tuesday. He had acted of his own accord, it added.

No group has taken the credit for the raid, although there have been suggestions that it was carried out by a shadowy organisation called the Cheollima Civil Defence, which has declared itself to be a government in exile. Also known as Free Jeoson, it claims to be planning the overthrow of the government of Kim Jong-un.