HELSINKI (AP) — A 25-year-old foreign student has been arrested in Norway on suspicion of espionage, including illegal eavesdropping through various technical devices.

Norway’s domestic security agency, known by its acronym PST, told Norwegian media that the man, who was arrested on Friday, was charged in court on Sunday with espionage and intelligence operations against the Nordic country.

The man, whose identity and nationality haven’t been disclosed, has pleaded not guilty in initial police questioning. Norwegian authorities haven’t said which country the man was allegedly spying for.

“We don’t quite know what we’re facing. We are in a critical, initial and vulnerable phase of the investigation,” PST lawyer Thomas Blom was quoted as saying by Norwegian public broadcaster NRK. “He (the suspect) is charged with using technical installations for illegal signal intelligence.”

Police have seized from the man a number of data-carrying electronic devices, which the PST is now investigating. The suspect is a student, but he’s not enrolled at an educational institution in Norway, and he’s been living in Norway for a relatively short time, according to PST.

Citing the arrest order, NRK said the suspect had allegedly been caught conducting illegal signal surveillance in a rental car near the Norwegian prime minister’s office and the defense ministry.

According to a court decision, the man has been imprisoned in pretrial custody for four weeks with a ban on receiving letters and visits. Security officials said the suspect wasn’t operating alone.

In its previous assessments, PST has singled out neighboring Russia, China and North Korea as state actors that pose a significant intelligence threat to Norway, a nation of 5.4 million.