Pop megastar Taylor Swift on Wednesday broke her silence about the cancellation of three Vienna concerts over an alleged suicide attack plot, saying the incident filled her with "fear" and "guilt."

"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 had planned on coming to those shows," the American said in a post on social media platform Instagram.

The Vienna shows, part of the European leg of Swift's record-breaking "Eras" tour, were cancelled after authorities warned of a terror plot by sympathizers of the Islamic State armed group.

Police have detained three suspects over the alleged attack threat, with the United States saying it shared intelligence to assist in the investigation.

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 Austrian domestic intelligence agency (DSN) head Omar Haijawi-Pirchner.

In the social media post Wednesday, Swift thanked the authorities.

"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," she said.

The European leg of Swift's sold-out tour began in Paris in May and has taken in Sweden, Portugal, Spain, Britain, Ireland, the Netherlands, Switzerland, Italy, Germany and Poland.

It concluded on Tuesday with five shows at London's Wembley stadium.