Authorities said the suspect, identified for legal reasons only as Samy W., was flown to Stuttgart and taken into custody on Friday.

The teenager allegedly joined the "IS" group and underwent weapons training to prepare him for combat. Prosecutors say he had "misgivings" about fighting, however, and fled to a Kurdish-controlled region of northern Syria in July, before he continued to Turkey where he was arrested.

Concern over radicalization

In a similar case last week, a court in the western German city of Düsseldorf sentenced a 22-year-old man to two and a half years in prison after he was found guilty of joining "IS."

As the number of Westerners traveling abroad to fight alongside the terror group increases, so has concern over the radicalization of Muslim youths.

According to Hans-Georg Maassen, the head of Germany's domestic intelligence agency, the number of ultra-conservative Salafist Muslims in Germany rose to 7,900 last month, compared to 7,500 in June.

The intelligence service has warned that Islamists may now be attempting to mobilize some of the thousands of asylum seekers who have arrived in Germany in recent months.

Authorities have also launched raids on suspected recruitment centers.

ksb/jm (dpa, epd)