The agency said that intelligence it discovered disrupted the plans - which allegedly were linked to Islamic State - and led to arrests made by Austrian authorities.

CIA deputy director David Cohen addressed the failed plot during an annual intelligence and national security summit held this week in Maryland.

"They were plotting to kill a huge number - tens of thousands of people at this concert, including I am sure many Americans - and were quite advanced in this," Mr Cohen said.

"The Austrians were able to make those arrests because the agency and our partners in the intelligence community provided them information about what this ISIS-connected group was planning to do."

Austrian officials said the main suspect, a 19-year-old Austrian man, was inspired by the Islamic State group.

He allegedly planned to attack outside the stadium, where upwards of 30,000 fans were expected to gather, with knives or homemade explosives. Another 65,000 fans were likely to be inside the venue.

Investigators discovered chemical substances and technical devices during a raid of the suspect's home.

Austria's interior minister Gerhard Karner previously said help from other intelligence agencies was needed because Austrian investigators, unlike some foreign services, can't legally monitor text messages.

The suspect's lawyer claimed Austrian authorities were "presenting this exaggeratedly" in order to get new surveillance powers.

Swift's three planned concerts earlier this month were cancelled after the plot was foiled, devastating fans of the 34-year-old star - including some who had travelled across the globe.

The main suspect and a 17-year-old were taken into custody on 6 August, the day before the cancellations were announced. A third suspect, 18, was arrested on 8 August.

Their names have not been released in line with Austrian privacy rules.

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Swift broke her silence on the cancellations last week after her London shows - the next stop after Vienna - had concluded.

"Having our Vienna shows cancelled was devastating," she wrote in a statement posted to Instagram. "The reason for the cancellations filled me with a new sense of fear, and a tremendous amount of guilt because so many people had planned on coming to those shows."

She thanked the authorities - "thanks to them, we were grieving concerts and not lives," she wrote - and said she waited to speak until the European leg of her Eras Tour concluded to prioritise safety.

"Let me be very clear: I am not going to speak about something publicly if I think doing so might provoke those who would want to harm the fans who come to my shows," she wrote.

The shows in London came on the heels of a stabbing at a Swift-themed dance class that left three girls dead in Southport.

The Vienna plot also drew comparisons to a 2017 attack by a suicide bomber at an Ariana Grande concert in Manchester, England, that killed 22 people.

The bomb detonated at the end of Grande's concert as thousands of young fans were leaving, becoming the deadliest extremist attack in the UK in recent years.

Swift's record-smashing Eras Tour is on hiatus until autumn.