A teenager was arrested Tuesday and charged with making a threat against a high school in Prince George’s County, Md.

The county police said early Tuesday that a “newly-posted” threat had been posted against Crossland High School in the Temple Hills area. In a video afterward, police chief Henry P. Stawinski III said it was “a grave threat,” but did not elaborate.

Later in the day, police said they had located the person who made the threat. They said they had charged a male 14-year-old with making a threat of mass violence.

Police seaid he had no means of carrying out the threat. However, they said, they take seriously every threat of school violence even if it is determined to be a prank.