Austrian authorities are treating a teenager arrested last week as a potentially dangerous radical with connections to Islamic State (IS).
Interior minister Wolfgang Sobotka said the 17-year-old has told police that he supports the extremist group.
Mr Sobotka added the suspect had a "real communications network" and is someone with "weight" in radical circles.
A Swat team made the arrest in a Vienna apartment on Friday after what police said was a tip from a "foreign intelligence service".
Police said the suspect may have been close to carrying out an attack, but Mr Sobotka said on Monday there are no indications that the teenager had "concrete" plans.
Another suspect thought to be linked to the Austrian is in German custody after his arrest on Saturday.