A former Danish defence minister said Tuesday he had been charged with leaking state secrets, in a case linked to a scandal regarding Denmark's collaboration with US intelligence.

Claus Hjort Frederiksen, who was defence minister between 2016 and 2019, wrote on Facebook that Danish intelligence officers had "presented me with a charge sheet." "The indictment is classified as secret so I'll keep that to myself," he said.

Earlier, the prosecutor's office said it had brought charges against a former member of the Danish parliament relating to "disclosing or passing on secrets important to national security".

It did not identify the accused by name. "I dispute having exceeded the limits of my extensive freedom of speech rights as a politician and I have not disclosed alleged state secrets. Period," the former minister wrote.

Hjort Frederiksen has been under investigation for leaking confidential information, but he enjoyed immunity as an MP until November when he did not seek re-election in legislative elections. The exact information he is believed to have leaked has not been made public.

In May 2021, an investigation by several Danish media outlets revealed that the US National Security Agency (NSA) used Danish underwater cables to spy on officials in France, Germany, Norway and Sweden until at least 2014. Former German chancellor Angela Merkel was among the NSA's targets.

The revelations sparked an international scandal and the four countries demanded explanations from Washington and Copenhagen.

A few months later, Hjort Frederiksen claimed in an interview with public broadcaster TV2 that the agreement on the use of the submarine cables was made in the late 1990s by US President Bill Clinton and Danish Prime Minister Poul Nyrup Rasmussen.

"That's what I understood. That's how it is. From what I know," he said at the time. The date of the trial has not yet been announced but is to take place in Copenhagen. Prosecutors have requested that it be held behind closed doors.

"The case involves highly classified information that cannot be disclosed openly," prosecutor Jakob Berger Nielsen said in a statement. "Despite the high level of public interest, it is the opinion of the prosecution that the work of the intelligence services takes precedence," he added. Hjort Frederiksen vowed that he would "fight to the outmost to keep (the doors of the trial) wide open."