The chief of Denmark's foreign intelligence unit, Lars Findsen, has been remanded into custody over his involvement in a case involving a leak of "highly classified" information, local media reported on Monday.

Four current and former employees of Denmark's two intelligence services were detained in December for leaking highly classified information. Findsen is the only one who remains in custody while the investigation continues.

The news emerged at a court hearing on Monday when a publication ban was lifted.

The case, about which authorities have published very little information, is being conducted behind closed doors, meaning that the exact charges and nature of the leaked information has not been made public.

According to public broadcaster DR, which cited unnamed sources, the case revolves around leaks of classified information to Danish media outlets.

DR reported in 2020 that the Danish Defence Intelligence Service had shared raw data from information cables with the U.S. National Security Agency, meaning the NSA may have had access to Danish citizens' personal data and private communications.

Last year, several other domestic media outlets published reports about Danish intelligence activities based on confidential information.

It is unclear how long Findsen will be kept in custody. The public prosecutor's office declined to comment on the case, and Reuters was not immediately able to contact Findsen or his lawyer.

In a separate case, Findsen and four other intelligence officials were suspended in August 2020 after an independent board overseeing the intelligence unit made accusations of serious wrongdoing. Last month those accusations were rebuffed by an investigating commission, and the suspensions were lifted.