According to NRK, the suspect, who was born in Norway, had voiced support for the Islamic State group and had been seen in school with the group's flag.

He was arrested on Thursday by Norway's PST internal security service, which is responsible for counter-terrorism, before being taken into provisional custody for two weeks on Friday.

The PST confirmed to AFP that it had made the arrest.

"He is suspected under the section of the Criminal Code relating to the preparation of a terrorist act," said Line Nyvoll Nygaard, a senior official with the agency.

Citing the "ongoing investigation," a PST spokesperson declined to comment further.

The youth's lawyer, Knut Lerum, told AFP that the suspect denies the accusations.

NRK quoted PST documents as saying the teenager planned to detonate explosives at NATO's Joint Warfare Centre in Jatta, Stavanger, in southwestern Norway.

Founded in 2003, the centre is involved in the US-led training of senior alliance officers and the organisation of military exercises.

The teenager was arrested in the southwestern Rogaland region, where Stavanger is located.