The Austrian Federal Ministry of the Interior announced the arrest of two individuals suspected of planning a terrorist attack in Vienna—possibly at one of pop superstar Taylor Swift’s concerts—prompting cancellation of the shows shortly after the police made the announcement.

According to Swift’s Era’s Tour website, the singer had three days of performances scheduled in Vienna beginning Aug. 8.

Barracuda Music, a concert promotion company in Vienna, said that the shows were canceled after “confirmation from government officials of a planned terrorist attack at Ernst Happel Stadium.”

The company added in posts on social media and on their website that they had, “no choice but to cancel the three scheduled shows for everyone’s safety” and all tickets would be refunded within the next 10 business days.

The government ministry said earlier in the day that the arrests were the result of a “significant police operation” which led to the seizure of chemical substances.

In a press release, Franz Ruf, director general for public security in the Austrian Ministry of the Interior, said “a targeted raid was carried out” on the morning of Aug. 7 following an order from a local prosecutor’s office. He said in an accompanying press conference there was suspicion of explosives located near the suspect’s residence.

Authorities said the operation led to the arrest of a 19-year-old Austrian citizen in a city about one hour south of Vienna along with another suspect in Vienna.

“Both suspects had become radicalized on the internet and had taken concrete preparatory actions for a terrorist attack,” the authorities said in the press release, according to an English translation. “The main suspect had sworn an oath of allegiance to [the Islamic State] on the internet and chemical substances were seized in his apartment during a house search.”

The release said that based on current assessments by authorities regarding terrorist and extremist acts, the Vienna State Police Directorate have increased security precautions, particularly at major events such as the Swift concerts. The terror alert level in Austria remains high and is continuously evaluated, the authorities added.

State Police President Gerhard Pürstl described the security enhancements, noting that “increased attention is being paid to anti-terror components ... and measures within the framework of robust area protection during events in the stadium and the surrounding area.”

Additional security protocols include extensive video surveillance and airspace monitoring, the authorities said. Vienna police have also organized thorough searches in preparation for these events and maintain close communication with event organizers.

Access to event venues will be tightly controlled for visitors and others seeking entry into events, the authorities said, while traffic barriers will also be implemented to restrict parking access to authorized personnel only.

The U.S. Embassy in Vienna posted a message on social media for American Taylor Swift fans attending her concerts in Vienna earlier in the week, encouraging tourists to stay safe by registering for emergency alerts online.

Swift had not yet commented on the reports as of the afternoon of Aug. 7.