The 19-year-old main suspect was arrested in Ternitz, south of Vienna, and the second suspect 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 (APA) 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 cancellations came hours after authorities said security measures for the Swift concerts would be stepped up. Ruf said that there would be a special focus on entry checks, among other things, and concert-goers should expect longer waits.
Vienna Police Chief Gerhard Purstl also said that, while any concrete danger had been minimized, an abstract risk justified raising security.
Austrian Interior Minister Gerhard Karner said the country's police and intelligence service had "contributed everything to ensure safe events" and that the organizer made the decision to cancel the concerts, APA reported. He said there had been "close networking with foreign security authorities."
Barracuda Music said that "all tickets will be automatically refunded within the next 10 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.
Swift fans took to social media to express their devastation at missing out on one of the superstar's shows. Some who posted on social network X lamented months of now-wasted efforts to make friendship bracelets and pick out fashionable outfits for the performance.
In 2017, an attack at an Ariana Grande concert in Manchester, U.K., killed 22 . 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 were injured.
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.
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