Three violent attacks at Polish schools this week were driven by the online glorification of violence, Prime Minister Donald Tusk said.
The incidents left one woman dead and several children injured.
Tusk described the stabbings as "spontaneous actions inspired by online activity" in a Sunday crisis meeting with security services.
Poland police have now arrested 117 people across the country for weapon possession or threatening to attack schools, after searching tens of thousands of schools.
A woman was arrested on Saturday after injuring three people while attacking a 17‑year‑old girl in Warsaw.
The police raid followed two prior stabbings, one of which killed a female caretaker at a primary school in Leszczydol‑Nowiny, north of Warsaw.
Tusk stressed that "we are not dealing with any large‑scale organised group." He added that there has been a global rise in fascination with violence and the "mass killers who have become idols online."
He also said the attacks were "nihilistic violence" linked to the extreme right, noting that some detainees are active in ultraright circles.
On Wednesday a 19‑year‑old student attacked and injured nine people at a vocational school in central Mazovia, and a day later a 15‑year‑old entered a primary school and killed a 37‑year‑old caretaker.
Interior Minister Marcin Kierwiński said a 17‑year‑old was detained in Sierpc after publicly threatening to do something "dangerous".
Hundreds of police officers visited schools nationwide to quell rumors of a potential "Bloody Friday" of attacks spurred by an online challenge.
Government security services convened a special meeting Sunday after receiving intelligence about a possible attack on PM Tusk and Defence Minister Władysław Kośniak‑Kamysz. A spokesperson called the threat "deadly serious."
