Mertkan G, was arrested in October 2014 and allegedly had contact with supporters of ISIS and Al-Qaeda.

"In addition he is suspected of obtaining instructions on how to make an explosive device from an Al-Qaeda website in order to carry out an attack in Vienna," the court said.

Mertkan G emigrated from Turkey in 2007 and wanted to carry out the attack before travelling to join "holy war" in Syria and was in contact with ISIS recruiters in Vienna.

He arrest at time of buying materials for making a bomb.

Unconfirmed press reports said that ISIS militants had offered to pay him 25,000 euros ($27,250) if he managed to carry out the attack.

In common with other European countries, Austria has seen a steady flow of people leaving or attempting to leave the country in order to join ISIS militants in Syria and Iraq.

According to the Austrian Interior Ministry, more than 200 have done so, including some women and minors. Around 70 have since returned, several of whom are in custody awaiting trial.