Terrorists plotted to kill "tens of thousands" of people at Taylor Swift's concert in Vienna.

The 34-year-old pop star was forced to cancel three dates on her 'Eras' tour in the Austrian capital earlier this month due to a planned attack at the Ernst Happel Stadium before officials arrested three teenagers, and a CIA official has now revealed the US intelligence agency played a major part in thwarting the "quite advanced" plot.

CIA Deputy Director David Cohen is quoted by ABC News as saying: “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.

"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.

“I can tell you within my agency, and I’m sure in others, there were people who thought that was a really good day for Langley. And not just the Swifties in my workforce.”

Taylor recently admitted she feels a "tremendous amount of guilt" over the planned attack.

In a lengthy statement shared on Instagram following her final European dates of the 'Eras' tour in London, she wrote in part: "Walking onstage in London was a rollercoaster of emotions.

"Having our Vienna shows cancelled was devastating. 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. But I was also so grateful to the authorities because thanks to them, we were grieving concerts and not lives. I was heartened by the love and unity I saw in the fans who banded together."

The 'Anti-Hero' songstress therefore decided to put "all of [her] energy" into keeping all those who came to subsequent concerts as safe as possible and her efforts all resulted in receiving the "most giant bear hug" from all of her audiences at Wembley Stadium.

She said: "I decided that all of my energy had to go toward helping to protect the nearly half a million people I had coming to see the shows in London. My team and I worked hand in hand with stadium staff and British authorities every day in pursuit of that goal, and I want to thank them for everything they did for us.

"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.

"In cases like this one, ‘silence’ is actually showing restraint, and waiting to express yourself at a time when it’s right to.

"My priority was finishing our European tour safely, and it is with great relief that I can say we did that."