A suspect confessed to a plot using explosives and other weapons to kill as many attendees as possible, security officials said. The singer’s three-concert Vienna run was canceled.

Five people stand outside a large modern building. Visitors talk to security staff outside the Ernst Happel Stadium in Vienna on Thursday after all three Taylor Swift concerts scheduled to take place there were canceled by the event’s promoters.Credit…Max Slovencik/EPA, via Shutterstock

Less than 24 hours after the arrest of two teenagers who the Austrian authorities say planned to attack a Taylor Swift concert in Vienna, security officials outlined a picture of a terrorist assault designed to kill as many people as possible.

Barracuda Music, the promoter for the singer’s three-concert Vienna run, canceled the gigs on Wednesday night. The events, which were scheduled to start Thursday, had been expected to draw more than 200,000 fans from across the world.

The main suspect is a 19-year-old man who was radicalized online and swore an oath of allegiance to the Islamic State, Franz Ruf, the head of public safety in Austria, told a news conference on Thursday. Mr. Ruf said the suspect had confessed to the plans shortly after being arrested, giving the police a detailed insight into his intended acts, which included using explosives and weapons to kill as many concert attendees as possible.

Searching the man’s home, where he lived with his parents, the police found explosives, timers, machetes and knives, Mr. Ruf said.

A 17-year-old suspected of being an accomplice was known to the police and had recently started a job for a events service provider that was working at the Ernst Happel Stadium, where Ms. Swift was scheduled to play. He was arrested on Wednesday at the stadium, Mr. Ruf said.

A 15-year-old boy who was also brought in for questioning confirmed many details of the main suspect’s confession, Mr. Ruf said, adding that the police believed that the boy was not an active participant in the plot, but knew of its details.

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