VIENNA (AP) — Organizers of three Taylor Swift concerts in Vienna this week called them off on Wednesday after officials announced arrests over an apparent plot to launch an attack on an event in the Vienna area such as the concerts.

Swift was scheduled to play at the Austrian capital’s Ernst Happel Stadium on Thursday, Friday and Saturday as part of her Eras Tour.

Event organizer Barracuda Music said in a post on its Instagram channel late Wednesday that “we have no choice but to cancel the three scheduled shows for everyone’s safety.” It cited government officials’ “confirmation” of a planned attack at the stadium.

Earlier Wednesday, authorities said they had arrested two suspected extremists, one of whom appeared to be planning an attack on an event in the Vienna area such as the upcoming concerts.

The 19-year-old main suspect was arrested in Ternitz, south of Vienna, and the second person in the Austrian capital.

Franz Ruf, the public security director at Austria’s interior ministry, said that authorities were aware of “preparatory actions” for a possible attack “and also that there is a focus by the 19-year-old perpetrator on the Taylor Swift concerts in Vienna,” the Austria Press Agency reported.

Ruf said the 19-year-old had pledged an oath of allegiance to the Islamic State group.

The Austrian citizen is believed to have become radicalized on the internet. Ruf said that chemical substances were secured and were being evaluated. He didn’t give more details.

The cancelation came hours after authorities said security measures for the Swift concerts would be stepped up. Ruf said that there would be a special focus among other things on entry checks and concertgoers should plan a bit more time.

Vienna police chief Gerhard Pürstl said at the same time that, while any concrete danger had been minimized, an abstract risk justified raising security.

Barracuda Music said that “all tickets will be automatically refunded within the next 10 business days.” The same wording was posted under the Vienna dates on Swift’s official website.

The Vienna stadium had been sold out for the planned concerts, APA reported, with an estimated 170,000 fans expected for the concerts in Austria.

In 2017, an attack at an Ariana Grande concert in Manchester, England killed 22 people. Suicide bomber Salman Abedi set up a knapsack bomb in Manchester Arena at the end of Grande’s concert as thousands of young fans were leaving. More than 100 people were injured. Abedi died in the explosion.

An official inquiry reported last year that Britain’s domestic intelligence agency, MI5, didn’t act swiftly enough on key information and missed a significant opportunity to prevent the bombing, the deadliest extremist attack in the U.K. in recent years.