German authorities have arrested a Syrian man accused of belonging to a unit of the Islamic State group in his homeland that kidnapped and killed opponents, prosecutors said Wednesday.

The man, identified only as Asmael K. in line with German privacy rules, was arrested in the western city of Essen on Monday. He is accused of membership in a foreign terrorist group.

The suspect is accused of joining IS in Syria in late 2013, swearing a public oath of loyalty to the extremist group and belonging to an IS unit that "kidnapped and executed opposing fighters and otherwise unwanted people," federal prosecutors said in a statement.

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German authorities arrested a Syrian man who was allegedly a member of the Islamic State group (Fox News)

They didn't give further details on his alleged role in that group, or say when he came to Germany.

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A judge on Tuesday ordered him kept in custody pending a possible indictment.