Taylor Swift canceled three concerts in Vienna after Austrian authorities arrested two people, accusing them of planning attacks on large-scale gatherings – including the singer’s shows – in the European capital. The arrests come amid a string of similar terror threats targeting major events in Europe this summer. One of the suspects is a 19-year-old who allegedly pledged allegiance to the Islamic State, authorities said.

That suspect, an Austrian citizen, was arrested Wednesday in the town of Ternitz. “We have identified relevant preparatory actions and also that a focus of the 19-year-old was the Taylor Swift concerts in Vienna,” said Franz Ruf, the public security director at Austria’s interior ministry, in a joint news conference on Wednesday with police chief Gerhard Purstl. No information was shared about the second suspect.

Swift’s concerts were scheduled for Thursday, Friday and Saturday at Ernst Happel Stadium and were expected to draw more than 150,000 people across all three nights. Ruf said the arrested people were radicalized online, and that officers found chemical substances in the first suspect’s home. Investigators are working to determine if those substances could have been used to construct a bomb, according to authorities.

Though Purstl said during the Wednesday news conference that security would be increased for the concerts, including police dog units and anti-terror teams, the official Taylor Nation Instagram account indicated later on .