The chief of Denmark's Defense Intelligence Service (FE), Lars Findsen, is in custody for more than a month over an alleged leak.
According to reports on local media on Monday, the leak involved "highly sensitive" information.
Last year there was allegations that Danish intelligence colluded with the US National Security Agency (NSA) to spy on European leaders and private Danish citizens.
"The news only emerged at a hearing behind closed doors at Copenhagen Magistrate's Court, when a publication ban was lifted. Findsen's name was revealed at his own request," DW reported.
On Sunday, Reuters reported that four current and former employees of the two Danish intelligence services — foreign and domestic — had been detained for leaking highly sensitive information.
"The arrests are the results of a lengthy investigation into leaks from the intelligence services," the Danish Security and Intelligence Service said adding that the investigation would continue while the cases had been handed over to prosecutors.
Findsen was the only one of them to remain in custody as the investigation proceeds.
"I want the charges brought forward and I plead not guilty. This is completely insane," Findsen told reporters at the hearing.
Public broadcaster DR cited unnamed sources as saying the case related to the leaking of classified information to Danish media outlets.
In 2020, DR reported that the FE had shared raw information cable data with the NSA. As a result, it said, the NSA may have had access to Danish citizens' personal data and private communications.
Authorities have published very little information on the investigation, which is being conducted behind closed doors. The exact charges and the content of the leaked information has not been made public.
It was unclear how long Findsen will be kept in custody, although he was said to have been already detained for more than a month. The Danish public prosecutor's office has declined to comment on the case.
Denmark has two intelligence agencies, the Police Intelligence Service (PET) and the FE, focusing respectively on domestic and foreign intelligence.
Findsen, 52, headed PET from 2002 to 2007 and the FE from 2015 to 2020, when he was suspended over an internal report. The document criticized a possible case of illegal spying on Danish citizens, although Findsen was recently cleared by a commission.
