THE HAGUE, Netherlands (AP) — Dutch Prime Minister Mark Rutte said Friday that threats that forced a teacher in the port city of Rotterdam to go hiding after some students objected to a political cartoon displayed in his classroom must not be tolerated.

Rutte spoke hours after Rotterdam police said they had arrested an 18-year-old girl on suspicion she posted a message on social media that “incited others to commit crimes" directed at the school and teacher.

“The fact that at this moment teachers are being threatened because they paid attention in their lessons to the discussion around cartoons is absurd and we must not tolerate it,” Rutte said.

Dutch lawmakers have reacted angrily to reports that the teacher, who has not been publicly identified, came under threat because of a cartoon that reportedly had been on display for five years at his classroom at the Emmauscollege in Rotterdam.

Police tweeted Nov. 3 that the teacher had been threatened and that they were treating the case “extremely seriously.” Police did not elaborate on the nature of the threats.

The threat comes weeks after French teacher Samuel Paty was beheaded outside his school in a Paris suburb Oct. 16 by a teenage refugee of Chechen origin for showing the caricatures in a civics class.

In a statement posted on its website Friday, the Rotterdam school said it is “completely unacceptable that a discussion between teachers and students is hijacked by people from outside who use this to make unfounded threats.”

The cartoon, titled “Immortal” was drawn in the aftermath of the deadly 2015 attack on the offices of the French satirical weekly newspaper. The cartoonist, Joep Bertrams, told Dutch daily Trouw this week that it is not a depiction of Islam's Prophet Muhammad. The drawing won a Dutch prize as the best political cartoon of the year in 2015.

Police and authorities have not detailed the exact circumstances of the case and why it escalated. Education Minister Arie Slob told broadcaster NOS earlier this week that there was a discussion about the cartoon “that took on its own dynamic because of things that went on social media.”

The school said that just as important as increasing the knowledge of students, it “is our task to guide them to a place in society where they can find their way in freedom and with respect for each other. Teachers discuss this with students every day.”

Rutte, who teaches part-time at a school in The Hague, said: “I want to emphasize here how essential it is for all of us to be able to discuss a topic like freedom of speech in our classrooms without any outside pressure. Because, yes, it can be complicated when someone has an opinion that grates against your worldview or with your religious beliefs,"

But, he added, "the other person may say so freely. Nobody has the right not to be insulted.”