The United States provided the tip of the threat to this week's "Eras" tour concerts which have been cancelled, the US administration said.
Austrian police on Wednesday arrested suspects aged 19 and 17 over a plot to kill "a large number of people" at one of the three gigs, which were meant to start Thursday, according to authorities.
Interior Minister Gerhard Karner said that "an 18-year-old Iraqi close to the main suspect and who pledged allegiance to the Islamic State group was arrested" in Vienna on Thursday.
The main suspect, a 19-year-old Austrian with North Macedonian roots, had allegedly confessed, saying he "intended to carry out an attack using explosives and knives", according to domestic intelligence agency (DSN) head Omar Haijawi-Pirchner.
The second suspect, a 17-year-old Austrian of Turkish and Croatian origin, had been hired by a facility company that was to have worked at the Ernst Happel Stadium where Swift was to perform, said Haijawi-Pirchner.
Chancellor Karl Nehammer said there were "concrete and detailed" plans to commit a "bloodbath".
The White House on Friday confirmed the United States had provided intelligence to Austria to thwart the plot.
"We work closely with partners all over the world to monitor and disrupt threats," National Security Council spokesman John Kirby told reporters.
The Austrian army's intelligence service was warned of a looming attack 10 to 15 days prior by two unspecified countries that helped it foil the plot, news agency APA had reported.
Swift was set to perform three shows from Thursday to Saturday as part of her mega record-breaking "Eras" tour.
The European leg of the sold-out tour began in Paris in May and has taken in Sweden, Portugal, Spain, Britain, Ireland, the Netherlands, Switzerland, Italy, Germany and Poland.
Her next concerts are at Wembley stadium in London from next Thursday and authorities have said they will go ahead.
In Austria, the shows had been expected to bring in some 100 million euros ($109 million) and gather 170,000 fans, according to APA estimates.
Swift has not yet commented on the decision to cancel the Vienna shows but said she was "completely in shock" after a deadly attack in Britain on July 29 at a Swift-themed dance class.
Three girls were killed and five people seriously wounded in the mass stabbing at the class in Southport, England.
