Spanish media reports that the attackers held back the employees with a rope and stole a variety of objects before fleeing in luxury vehicles.
During the attack, a Korean woman managed to escape the embassy and her screams alarmed the residents who had called the police, the newspaper said. When police tried to knock on the door, they were told that nothing was going on.
The alleged attack occurred just a few days before US President Donald Trump and North Korean leader Kim Jong Un held their second summit in the Vietnamese capital Hanoi.
The meeting between Trump and Kim ended abruptly, partly because of disagreement over when UN sanctions should be lifted in exchange for steps to de-nuclearize Pyongyang. But Trump and his helpers said both sides had good conditions.
Police refused to disclose details of the embassy case, as the case is under investigation. The Spanish Interior Ministry said that it does not comment on any active investigations. CNN has dealt with the comment of the Spanish Ministry of Foreign Affairs.
A source from the US government said the Cheollima Civil Defense, a shadowy North Korean dissident group, was behind the attack.
The Washington Post first reported on the involvement of the CCD of the secret group, whose goal is to overthrow the Kim regime. The group did not respond to CNN's request for comment and did not publicly accept responsibility for the attack.
It is unclear why Kim Jong Nam was killed. However, when North Korea was behind the murder, it was not clear. Un looked at his brother and family as a potential threat to his leadership.
"The Cheollima Civil Defense has created credibility by acting swiftly and receiving Kim Han Sol, son of Kim Jong Nam, within days of his father's cruel murder," said Sung-Yoon Lee, a professor at the University of New York Fletcher School of Law at Tufts University and Diplomacy.
Connection to Kim Hyok Chol?
Spanish media cited anonymous sources speculating that the embassy incident may be linked to former North Korean Ambassador Kim Hyok Chol.