Vienna, Austria - The three suspects in the terrorist plot on Taylor Swift concerts in Vienna are to remain in custody for another month, a city court said on Friday.

A spokeswoman for the Vienna Regional Court said the trio would be held until at least September 23 due to the risk of collision and further offenses.

The 19-year-old main suspect and a 17-year-old accomplice are under investigation for membership of a terrorist organization.

The third suspect, aged 18, admitted to being a member of the Islamic State terror group but is not thought to have been involved in the plans to attack concert-goers at the Ernst Happel Stadium in early August.

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Investigators detained the main suspect two days before the first concert was due to take place on August 8, leading to the cancellation of the three gigs.

The 19-year-old, whose family is from North Macedonia, is accused of equipping himself with explosives, knives, and a machete in order to attack fans.

"Having our Vienna shows canceled was devastating," Swift wrote on Instagram in recent days. "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."

The 34-year-old pop star thanked authorities for uncovering the plot, writing: "Thanks to them, we were grieving concerts and not lives."