Police in Poland carried out a series of arrests of teenagers today, mainly for making threats to launch attacks against schools, authorities announced. Officials are seeking to calm fears sparked by online rumours about a “Bloody Friday,” following two knife attacks at schools within a period of two days.

Social media in Poland has been flooded with rumours that the attacks were linked to an online challenge. However, police said today that they had found no evidence to support these claims.

Yesterday, Thursday, a 15-year-old killed the caretaker at his former school and stabbed two other adults. On Wednesday, a 19-year-old also stabbed nine people at another school in the country.

The incidents have put the country’s authorities on high alert, with police deployed to 10,000 schools and the government warning about the spread of disinformation that could inspire others to commit similar acts.

“There is a great deal of emotionally charged disinformation circulating online, along with spontaneous reactions stemming from understandable concern, but there is no evidence of a nationwide ‘challenge’,” Poland’s Minister of Digital Affairs, Krzysztof Gawkowski, said in an interview with private television station TVN24.

“We cannot rule out the possibility that one, two or three people are talking in a group and making plans, or that someone might imitate the crime. However, there is no evidence of a threat from a group of people coordinating to harm someone today,” he added.

Police have announced the arrest of 10 people, mainly for making threats online. Among those arrested is a 13-year-old from Warsaw who posted a photograph of a knife in his class’s group chat and threatened some of his classmates.

Another teenager, aged 14, was arrested at his school in the Polish capital. A knife and flares were found in his possession. Two 15-year-olds from Pruszków County were also arrested after uploading a video online in which they made threats.