In its statement on Thursday, the PET said that four individuals had been arrested the day before during “searches at various addresses” in Denmark. It did not disclose the identities of the four suspects, but said they were all current or former members of Danish intelligence agencies. At least one of them is believed to be a current or former employee of the PET itself. Denmark’s external intelligence agency, the Danish Defense Intelligence Service (FE, or DDIS in English), is also involved, according to reports.

The four suspects are accused of having disclosed “highly classified information from the intelligence services”, according to the information made available by the PET on Thursday. However, PET officials declined requests to discuss further details about the case, stating only that the arrests came after a lengthy counterintelligence investigation, which continues at this time. All four suspects have now been charged with violating Section 109(1) of the Danish Criminal Code, which is the standard law used by Danish prosecutors in espionage cases.

The last major counterintelligence case in Denmark was in 2012, when a Finnish professor at the University of Copenhagen, Timo Kivimäki, was convicted and sentenced to a short prison sentence for spying for Russia. Kivimäki, who today continues to work as an academic, claims that he carried out contractual consulting work for the Ministry of Foreign Affairs of the Russian Federation, but denies that he knowingly contacted Russian intelligence operatives in the course of his consulting duties.