Spain has issued two international arrest warrants after the extraordinary details of an alleged attack on the North Korean embassy in Madrid were revealed by a judge.

Information regarding what happened in the incident at the embassy last month had been scarce, but it was thought to have involved a group identifying themselves as human rights activists working to bring down the regime of Kim Jong-un.

Now, a report by a National Court judge in Spain claims that an investigation has found 10 activists forced their way into the embassy using fake guns, knives and balaclavas, tied up and gagged staff including the North Korean envoy and stole hard drives and documents.

The judge names suspects in the break-in, and identifies the alleged leader of the activists as Adrian Hong Chang, a Mexican citizen and US resident who helped co-found an aid organisation for North Korean defectors.

In his report, which was unsealed on Tuesday, Judge Jose de la Mata says Hong Chang and the other activists were able to flee Madrid after the attack - even after a woman escaped the alleged hostage situation - by posing as embassy officials and telling police nothing was wrong. The activists then drove away in embassy vehicles.

Members of the group made their way to Lisbon and then flew to New York, according to the judge. Once there, they contacted the FBI and sought to pass on information about North Korea obtained in the raid.

The alleged attack, on 22 February, came a week before Mr Kim’s high profile meeting with US president Donald Trump in Hanoi. There has previously been speculation that the incident was linked to the former North Korean envoy to Spain, Kim Hyok Chol, who is now the country’s top nuclear negotiator with the US.

The Washington Post reported earlier this month that a dissident group, Cheollima Civil Defense, had carried out the raid.

On its website on Tuesday, the group claimed involvement but said it was not an attack and that the group had been invited into the embassy. The group, which campaigns for the removal of the Kim dynasty in North Korea, said no one was gagged or beaten and that no governments were involved.

In his report, the judge said the current North Korean envoy, So Yun Sok, was encouraged by the activists to defect. He was gagged and bound after he refused to do so, it was claimed.

In Spain, a High Court judge can order an investigation into an incident with a view to bringing charges. No charges have yet been brought in the case but an official with Spain's National Police told the Associated Press that arrest warrants were issued for Hong Chang and one other suspect.

A judicial source also told the Reuters news agency that judge Jose de la Mata plans to request the extradition from the United States of members of the group. His report identified another as YS citizen Sam Ryu, and others as South Korean citizens.

State Department spokesman Robert Palladino said the US government was not involved in the raid. ”The United States government had nothing to do with this," he told a regular news briefing, stressing that the United States called for the protection of all embassies, adding that further questions should be put to the Spanish authorities.

The FBI said in a statement it was "our standard practice to neither confirm nor deny the existence of an investigation", adding that the agency had a strong working relationship with Spanish law enforcement partners.

Sung-Yoon Lee, a North Korea expert at Tufts University in the US, said it was “shocking” that the names of those allegedly involved in the raid had been released by the Spanish authorities.

He said it put the lives of members of the group at risk of North Korean reprisals.

"It seemed clear to me that the FBI had initially taken the position that the intel assets the group had retrieved at the embassy warranted the protection of the identities of the group," he told Reuters.

"Observing this extraordinary situation unfold, who in the future would collaborate with the United States government were they ever to come into possession of high-value intelligence on North Korea obtained illegally? Lee asked.