Berlin - German police are investigating a Syrian doctorate student in detention for having allegedly planned a bomb attack, reports say.
The 36-year-old man was previously already probed over suspected ties to the Islamic State group, said public broadcaster Hessischer Rundfunk.
Prosecutors have broadened their investigation after finding bomb-making instructions in his possession.
The suspect, who was studying for a doctorate at western Germany's Darmstadt Technical University, was detained last year over a video broadcast online in which he allegedly voiced his support for ISIS.
Investigators had confiscated his mobile phone and other electronic devices and subsequently found the bomb-building instructions.
But his lawyer has argued that the man downloaded those instructions in 2014 and that this did not qualify as proof he was planning an attack.
Germany is on high alert for jihadist attacks following a string of assaults last year, the deadliest of which was an ISIS-claimed December 19 truck rampage through a Berlin Christmas market that killed 12 people.