An 18-year-old Iraqi national was detained in Vienna in connection with investigations into an alleged plot to attack a Taylor Swift concert in the Austrian capital, Austria's interior minister said on Friday.

The Iraqi comes from the same circle as the main suspect, a 19-year-old Austrian with North Macedonian roots, Interior Minister Gerhard Karner said.

The Iraqi suspect swore allegiance to the Islamic State (IS) jihadist group on Aug. 6, but it remains unclear whether he had a direct link to the planned attack, Karner said.

More suspects will be questioned and properties searched as investigators continue to look into the plot, he added.

The main suspect, who had also vowed loyalty to IS, was planning a lethal assault among the estimated 20,000 "Swiftie" fans set to gather outside Vienna's Ernst Happel Stadium, prompting the cancellation of all three shows due to security concerns.

The 19-year-old, who quit his job less than two weeks before the planned attack, saying he "had big plans", has made a full confession in custody, according to authorities.

Two other Austrian youths aged 17 and 15 were detained on Wednesday over the alleged plot.

The 17-year-old, who had been given a job with a company that was providing services at the stadium, has so far refused to give evidence, according to Karner.

The boy, who also appears to have been radicalised, was already known to authorities.

The 15-year-old continues to be questioned intensively by police, Karner added.

Austrian authorities are reported to have received information about the Swift concert threat from U.S. intelligence, as Austrian law does not allow the monitoring of instant messaging apps, which the suspects had used to communicate.

"Cooperation with foreign partners and services is essential and reciprocal. This made it possible to prevent a tragedy in Vienna," Austrian Chancellor Karl Nehammer said.

Swift, whose next scheduled performance is in London next week, has not commented on the concert cancellations.

British police have said there is nothing to indicate that the Vienna plot would have any effect on the London show.