A 23-year-old man stabbed five passersby in southern Austria on Saturday (local time) in what police said was a random attack that left a 14-year-old dead and four others injured.
The suspect was detained in the city of Villach, where the attack took place, police said.
He is a Syrian national with legal residence in Austria, they said.
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Police spokesperson Rainer Dionisio said a motive was not immediately known.
He added that police were investigating the attacker's personal background. "We have to wait until we get secure information," he said.
The issue of migration has taken centre stage in many European countries, with far-right parties making inroads in elections.
In Austria, migration was a prominent topic leading up to last year's election, which resulted in the far-right Freedom Party securing its first national election victory since World War II.
On Saturday, police in neighbouring Germany said a 2-year-old girl and her mother died two days after being injured in a car-ramming attack during a labor union demonstration in Munich. It marked the fifth attack involving immigrants in Germany over the past nine months, with migration becoming a significant issue ahead of upcoming elections on February 23.
A 42-year-old man who works for a food delivery company witnessed the incident from his car, police said. He drove toward the suspect and helped to prevent things from getting worse, Dionisio told Austria's public broadcaster ORF.
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The victims were all men, with two seriously injured and two sustaining minor injuries, police said.
Peter Kaiser, the governor of the Austrian province of Carinthia, expressed his condolences to the family of the 14-year-old victim.
"This outrageous atrocity must be met with harsh consequences. I have always said with clarity and unambiguously: Those who live in Carinthia, in Austria, have to respect the law and adjust to our rules and values."
Erwin Angerer, a lawmaker for the far-right Freedom Party, said his party had been warning about the situation in Austria as a result of the country's "disastrous asylum policy".
Conservative party leader Christian Stocker said on the X social media platform that the attacker "must be brought to justice and be punished with the full force of the law."
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"We all want to live in a safe Austria, adding that this means political measures need to be taken to "avoid such acts of horror in the future," he said.
Leader of the Social Democrats, Andreas Babler, said on X that "the full force of the law" must be used. "Crimes like this one simply should not happen in our society."
Austria's Interior Minister Gerhard Karner was expected in Villach on Sunday morning, according to Austria's public broadcaster ORF.
Police said it wasn't clear whether the suspect acted on his own and continued to search for potential additional suspects. It was also not known whether there is any connection between the attacker and the victims.
According to the Austrian Ministry of Interior, 24,941 foreigners applied for asylum in Austria in 2024. The largest group of applicants comes from Syria, followed by Afghanistan.
Over the past two years, the number of asylum seekers has decreased significantly. In 2022, applications peaked at over 100,000, while approximately 59,000 individuals sought asylum in 2023.
Several European countries, among them Austria, said in December they are suspending decisions on asylum claims by Syrian nationals because of the unclear political situation in their homeland following the fall of Bashar Assad.
