The 19-year-old Austrian who masterminded a foiled plot to attack Taylor Swift fans at a concert in Vienna with a bomb or knife had pledged allegiance to the Islamic State, opens new tab militant group, authorities said on Thursday.

The main suspect, who has North Macedonian roots, made a full confession in custody, Austria's general director for public security Franz Ruf told a news conference.

He swore loyalty to the IS militant group's leader on the internet and kept chemicals and technical devices at his home in the town of Ternitz in preparation for an attack, Ruf added.

The 19-year-old, whose name was not given, was planning an attack with an explosive or knife among the estimated 20,000 "Swiftie" fans set to gather outside the stadium, said national intelligence head Omar Haijawi-Pirchner.

"There is currently no information that other concerts are subject to an explicit threat," he added at the news conference.

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

Swift's three concerts in Vienna, due to start on Thursday for a soldout 65,000 audience each, were cancelled, to the consternation of fans, many of whom had travelled far.

"It's just heartbreaking, just frustrating. But at the end of the day I guess it's for everyone's safety," said Mark del Rosario, who had flown from the Philippines for the show.

U.S. broadcaster ABC cited law enforcement and intelligence sources as saying Austrian authorities had received information about the Swift concert threat from U.S. intelligence.