An Austrian teenager arrested over an alleged plot to strike a Taylor Swift concert in Vienna planned to carry out a suicide attack that would have caused a "bloodbath" and had vowed loyalty to Islamic State (IS), authorities said on Thursday.

The 19-year-old man, who has North Macedonian roots, made a full confession in custody, Austria's general director for public security Franz Ruf told a news conference.

He swore allegiance to the IS group's leader on the internet and had chemicals, machetes and technical devices at his home in the town of Ternitz in preparation for an attack, Ruf added.

The suspect was planning a lethal assault among the estimated 20,000 "Swiftie" fans set to gather outside Vienna's Ernst Happel Stadium, said national intelligence head Omar Haijawi-Pirchner. Two other Austrian youths aged 17 and 15 were detained on Wednesday over the reported plot.

"The main perpetrator has confessed that he was supposed to carry out a suicide attack with two accomplices," said Austrian Chancellor Karl Nehammer.

"The suspects actually had very specific and detailed plans ... to leave a bloodbath in their wake."Authorities painted a picture of the main suspect having self-radicalised, transforming his appearance and sharing Islamist propaganda online. He quit his job on July 25, telling people he had "big plans", Ruf said.

One neighbour told Austrian broadcaster Puls24 that the suspect had kept himself to himself and had grown a "Taliban beard".

The 17-year-old suspect had been given a job with a company a few days ago that was providing services at the stadium, according to security officials.

Event organiser Barracuda Music said it had cancelled Swift's three concerts in Vienna, due to start on Thursday for a sold-out 65,000 audience each, in coordination with the singer's management team.

Fans, many of whom had travelled a long way to Vienna, expressed both dismay and understanding.

"It's just heartbreaking, just frustrating. But at the end of the day I guess it's for everyone's safety," said Mark del Rosario, who had flown from the Philippines to see the wildly popular U.S. singer.

Music world rocked

U.S. broadcaster ABC cited law enforcement and intelligence sources as saying Austrian authorities had received information about the Swift concert threat from U.S. intelligence.

It quoted the sources as saying that at least one of the suspects had pledged allegiance to ISIS-K, a resurgent wing of IS, on Telegram in June, though the plot was IS-inspired rather than directed by the group's operatives.

Austrian Interior Minister Gerhard Karner said foreign intelligence agencies had helped with the investigation, as Austrian law does not allow monitoring of messenger apps.

Event organiser Live Nation urged fans of Coldplay, which is due to play at the same stadium on Aug. 21, to stay calm and said it was in contact with authorities.

It did not comment on whether the show would take place.

British police said on Thursday, there was nothing to indicate that the planned attack in Vienna would have an impact on Swift's shows at Wembley Stadium in London next week.

"Concerts are often a preferred target of Islamist attackers, large concerts," said Karner, listing the 2015 attack on the Bataclan venue in Paris and the 2017 bombing at England's Manchester Arena where U.S. pop star Ariana Grande had played.

The plot in Austria also brought to mind a foiled plan by three IS-linked suspects to attack Vienna's gay pride parade last year.

Islamic State was largely crushed by a U.S.-led coalition several years ago after establishing a "caliphate" in large areas of Iraq and Syria, but has still managed some major attacks while seeking to rebuild and reinvent itself.

This week's shows were to be part of the record-breaking Eras Tour by American singer-songwriter Swift which started on March 17, 2023, in Glendale, Arizona, and is set to conclude on Dec. 8, 2024, in Vancouver, Canada.

Swift, 34, has not yet commented on the cancellations on her official Instagram account, which has 283 million followers.

Her fans were horrified at the threat, with some begging organisers to postpone the concert instead of cancelling it outright. Promoters have said they will pay back tickets.