Three violent attacks at Polish schools this week were driven by the "glorification of violence" online, Prime Minister Donald Tusk said.
The attacks have left one woman dead and others injured, including children.
"These are very often spontaneous actions inspired by online activity," Tusk said on Sunday, during a crisis meeting with security services.
Police have arrested 117 people across the country for possession knives or other weapons, or for threatening to attack schools or fellow students, after searching tens of thousands of schools.
A woman was arrested on Saturday after injuring three people while attacking a 17-year-old girl at an educational institution in the capital, Warsaw.
It came a day after thousands of police visited schools across Poland, following two stabbing attacks earlier in the week, one of which led to the killing of a female caretaker.
"We are not dealing with any group organized on a big scale," Tusk said on Sunday.
"In the past years and months, we have noted - globally and in Poland - a rise in the fascination with violence," he added.
The prime minister said the attacks were acts "nihilistic violence" associated with the extreme right.
"Some of the people detained are active in the ultraright environment," he said, adding that police had noticed a rise in online searches of Nazi content as well as of "mass killers who have become idols online".
On Wednesday, a 19-year-old student attacked and injured nine people at a vocational school in the central Polish province of Mazovian.
A day later, the 37-year-old caretaker was killed after a 15-year-old entered a primary school in Leszczydół-Nowiny, north of Warsaw.
Interior Minister Marcin Kierwiński also said a 17-year-old was detained in the town of Sierpc, north-west of Warsaw, after allegedly stating "on school grounds that he planned to do something... dangerous - that he intended to harm someone".
Thousands of Polish police officers visited schools nationwide to try to reassure pupils after the stabbings sparked rumours of a "Bloody Friday" of more attacks stemming from a supposed online challenge.
Meanwhile, Polish security services convened a special meeting on Sunday after receiving information about a potential attack on Tusk and Defence Minister Wladyslaw Kosiniak-Kamysz, a spokesperson said.
A special services spokesman said officials were treating the threat as "deadly serious".