The girl was reportedly arrested on Wednesday afternoon at her home in the village of Kundby on the island of Zealand.
TV2 reported that the 15-year-old is being charged under Denmark's terror laws. Charges include the possession of explosives, detonation of explosives and sanctioning or encouraging terror.
Central and West Zealand Police said early Thursday morning on Twitter that it would not immediately comment on the case:
In a subsequent tweet, the police district said that "a person" made a court appearance at 12pm but no additional information would be released.
The court appearance was held behind so-called 'double-locked doors', meaning all information is withheld from the media and the public.
According to TV2, the girl is Danish and had recently converted to Islam. One of the girl's neighbours told the tabloid BT that her Facebook page indicated that she supported Islam and the idea of converting Danes to the religion. TV2 also reported that the girl's profile page indicated that she was a member of Facebook group for ethnic Danish members of Hizb ut-Tahrir, an Islamic group that openly supports the establishment of a caliphate and that has been at the centre of numerous controversies in Denmark.
See also: Denmark looks to ban Hizb ut-Tahrir
BT subsequently reported that the girl's open Facebook profile didn't attempt to hide her support of jihad. The tabloid wrote that on her way into court on Thursday, the 15-year-old girl "looked more like a schoolgirl than a terrorist".
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The former head of the Danish Security and Intelligence Service (PET) called the case “unusual” in many ways.
“The authorities' handling is very atypical. Normally one gives information when it is case with these sorts of aspects in it,” Frank Jensen told TV2.
“The other thing is that this is about a girl as young as 15. On top of that, there are the explosives. It is quite unusual,” he added.