It was the country's first trial of a suspected IS militant deployed to Germany from Syria during the chaotic 2015 refugee influx -- in contrast to "lone wolf" attacks or plots by extremists who were radicalised elsewhere.
The defendant, identified only as 19-year-old Syrian national Shaas al-Mohammad, allegedly fought with the Islamist militia in his war-torn homeland for two years before arriving in Germany as a refugee in August 2015.
Dressed in a blue pullover and a black cap, Mohammad hid his face behind a folder as he took his seat in the courtroom. Two police trucks were parked outside the entrance, with officers armed with machine guns guarding the proceedings.
The trial comes just over two weeks after an IS extremist from Tunisia allegedly ploughed a truck through a Berlin Christmas market in an attack that killed 12 people.
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Prosecutors claim the defendant joined the jihadist group as a teenager in mid-2013, taking part in combat operations, handling an AK-47 assault rifle and supplying food to fighters.
He arrived in Germany near the peak of a mass influx of people fleeing Syria, Iraq and other crisis-torn countries that brought almost 900,000 asylum seekers to Europe's biggest economy in 2015.
Among the suspected targets was the area around the glass-domed Reichstag parliament building, the nearby Brandenburg Gate monument and the busy shopping square Alexanderplatz.
He then allegedly "passed the information about the potential attack targets onto his contacts at the IS", said the court in a statement.
"In addition, he arranged to send at least one person to Syria as a fighter and offered his services as a contact person for potential attackers in Germany," it added.