The lawyer of the main suspect in a foiled plot to carry out an attack at Taylor Swift concert in Vienna on Sunday sought to play down the seriousness of the plan, saying her client was only "playing with ideas".

Swift's three planned concerts this week were cancelled after Austrian authorities discovered a plot allegedly led by a 19-year-old to carry out an ISIS-inspired suicide attack at a soccer stadium where tens of thousands of fans were planning to attend the shows.

Austrian investigators said the youth had recently sworn a pledge to ISIS and had made a full confession after police raided his house, seizing chemicals, machetes and other devices the plotters planned to use in a bomb attack.

Lawyer Ina-Christin Stiglitz told Reuters the youth had only been involved with ISIS for the past month.

"It interested him," she said, suggesting that her client had not really intended to carry out a serious attack.

"It was just playing with ideas," she said. "He says the bomb wasn't of good enough quality, it wouldn't have worked."

He had researched online on how to build a bomb, she added.

Among three other teenagers Austrian police have detained in the investigation was a 17-year-old youth, whom Stiglitz said her client had described as his "best friend and neighbour".

Neighbours of the 19-year-old in the small town of Ternitz expressed shock at his arrest, describing him as reserved but friendly. One of few hints pointing to potential radicalization was that he had recently grown a long beard, they said.

Responding to a question about why he had changed his appearance, his lawyer said: "He wanted to be cool."

Chancellor Karl Nehammer said earlier that Austria's intelligence agencies should have greater power to monitor communications on messaging apps to stop extremists.