VIENNA (Reuters) -The main suspect among three Austrian teenagers detained over a planned attack on a Taylor Swift concert had pledged allegiance to the Islamic State militant group and had chemical substances at his home, authorities said. Austria's general director for public security Frankz Ruf told ORF radio on Thursday that chemical substances and technical devices, showing "concrete preparatory actions", were found at the 19-year-old's house in the town of Ternitz. He had sworn allegiance to Islamic State's leader, he added, citing internet evidence.