The court said that he was a flight risk and there was a danger he would try to rejoin jihadist fighters.
He was arrested at Vienna airport in mid-March with serious injuries, and told police that he had been wounded in a bomb attack in Raqqa, Syria.
His case is due to be reviewed on May 4th. Police and law officials are working to clarify how much a risk the teenager poses to Austrian security and to what extent he has been radicalized.
A psychiatric expert will examine whether he is traumatised or experienced any psychological damage after his time in Syria.
He may be charged with belonging to a terrorist organization, training to be a terrorist, and incitement to commit terrorist offences.
He is being held in Vienna’s Josefstadt prison and has recently been moved from a hospital ward to a young offenders section.
An international arrest warrant was issued after the teenager disappeared from Vienna in October 2014.
He had posted positive statements about Isis on his Facebook page and shortly after appeared in an Isis propaganda video – dressed in battle gear and armed.
Before he disappeared he had been training to become an insurance salesman, and had only converted to Islam in May.
He told police that he had “wanted to travel” and had been fooled by Isis recruiters into thinking that “one could live in Syria without joining the fighting – and have a house, a wife, and money”.
According to a report from Austrian broadcaster ORF he told police that he worked as an ambulance driver for Isis during the Battle of Kobane, and had taken injured fighters to hospital.
He told police that he had never been active in any battle and that after being seriously injured he had wanted to return to Austria, and that “he felt lucky to have survived the experience”.
He travelled to Turkey with a fake passport to seek medical treatment and then took a bus to Istanbul, where he made contact with his father in Vienna, who helped him secure an emergency passport and booked him a flight back to Austria.
His lawyer, Werner Tomanek, told Austria’s anti-terrorism office that his client “lost his spleen, a kidney and part of his lung” in the bomb attack.
He said that he “had fully confessed and wants to start over” and plans to cooperate fully with the Austrian authorities.