Security measures have been increased for Taylor Swift's concerts in Vienna, Austria, this week after two suspects were arrested for allegedly plotting a terror attack, authorities said.

A 19-year-old Austrian citizen was arrested Wednesday morning and a second suspect was arrested in the afternoon, according to Franz Ruf, director-general for public safety in the Ministry of the Interior.

The suspects allegedly radicalized themselves online, Ruf said at a press conference. The 19-year-old suspect allegedly pledged allegiance to the leader of the Islamic State in the beginning of July, Ruf said.

Vienna was a target of their planned attack and the 19-year-old suspect had a particular focus on Swift's Vienna concert, Ruf said.

The pop star has concerts in Vienna this Thursday, Friday and Saturday. The shows are expected to draw 65,000 concert-goers per day, with an additional 10,000 to 15,000 fans outside of the area, police said.

This is a developing story. Please check back for updates.