Norwegian police arrested a 16-year-old boy on suspicion of planning a terrorist attack, authorities said Wednesday, as local media reported that a preschool may have been the intended target.

Police prosecutor Lise Dalhaug told AFP the boy had been arrested after police received a tip from an "anonymous person abroad" who had "become aware of disturbing threats on various social media platforms."

Dalhaug said the boy had then been identified and arrested, and the case was being investigated as "preparation for a terrorist act."

Although the arrest took place in early June, it has not been made public until now.

Norwegian newspaper Aftenposten reported that the boy had plans to attack a preschool carrying axes and knives, but Dalhaug would not confirm the reports.

"He has talked about several targets," Dalhaug said, but she did not wish to say what they had been at this point.

Dalhaug said the boy had made the threat on different social platforms and that the investigation so far indicated "that he was alone in the planning."

The boy was a resident of the Vestfold region south of Oslo, she added. They hoped to complete the investigation by the end of September.

Asked about what kind of sentence the boy could face, Dalhaug said that "it is a very serious offense," meaning he would risk a "harsh prison sentence."