GENEVA — Swiss police say the 15-year-old suspect in the stabbing of an Orthodox Jewish man in Zurich over the weekend had appeared in a video expressing solidarity with the banned Islamic State group, and called himself a “soldier” in its self-described caliphate.

Zurich cantonal police security chief Mario Fehr told reporters Monday that authorities were investigating whether the teen, who was not identified, had acted alone or as part of a group. Officials said the suspect was a Swiss national.

“He refers to the IS (Islamic State), describes himself as a soldier of the caliphate,” Fehr said of the video that authorities had authenticated. He denounced the stabbing Saturday as a “terrorist” and “antisemitic” attack. The suspect was arrested at the scene.

In one video, the suspect referred to the attack in Arabic and called for a “battle against the Jews,” Fehr said.

Authorities said the 50-year-old victim was critically injured but his life was no longer in danger. Swiss police have stepped up security around certain sites with a Jewish connection as a precaution.

Switzerland was largely spared the extremist attacks across Western Europe and beyond in the mid-2010s, when the Islamic State group held large swaths of territory in Iraq and Syria and was drawing radical fighters and others to join its self-described caliphate.

Jewish leaders, rights groups, authorities and others in Switzerland and beyond have decried a surge of antisemitism since the deadly Oct. 7 attacks and hostage-takings by Palestinian militants in Israel.

In response, the Israeli government has led a ferocious military campaign in Gaza, where the attacks were launched, that has killed at least 30,000 people, according to the Health Ministry in the Hamas-run territory.