Police have arrested an minor in Leeuwarden for posting threatening messages to schools in the Friesian capital, in the third such incident this week.

The arrest on Wednesday came after the alarm was raised about messages on social media saying there would be shootings at schools in the city.  A police investigation led to the arrest of a minor in Leeuwarden who is currently being questioned.

Earlier on Wednesday a teenage girl was arrested in Lelystad after social media messages were circulated telling pupils at a school in IJsselstein they had “better not go to school”, accompanied by a picture of a gun.

On Monday a 14-year-old girl was arrested in Belgium after allegedly threatening schools in Breda. Those messages, according to local broadcaster Omroep Brabant, included a photograph of a pistol with bullets and the text “Everyone is going to die”.

Threats to schools have been circulating on social media since October, targeting schools in Amsterdam, Deventer, Lelystad, Breda, Woerden and Papendrecht. In 2023, schools in Rotterdam, Zwolle, Zaandam, Meppel and Os were warned about impending shootings, explosions or attacks.

Despite the difficulty of gauging the seriousness of the threats, experts have warned schools to take them “extremely seriously”.

“Schools have a pretty good understanding of their pupils but not of anonymous online posters,” Lynn Louwen, whose organisation School & Veiligheid advises schools in situations of acute threat, told the NRC.

It is up to the police to investigate if a threat is real, a police spokesman said.

None of the schools that were threatened this week were closed as a precaution and good communication with parents is key when trying to prevent panic reactions, Den Bosch teacher Lucien Schoonwater told the paper.

He was told some hours after the threats appeared that his pupils were not in danger and emphasised the police’s involvement to parents. “I had some worried phone calls but then it all settled down,” he said.

In most cases the motives of the poster remain a mystery, police said, adding that they are usually minors, who are possibly showing copycat behaviour prompted by other online threats.