The foreign ministry on Monday said that two women were among those seized, including a 16-year-old teenager, Linda Wenzel, who had run away from her home in the state of Saxony last year.
The source on Tuesday said that two others had now been confirmed as German citizens by consular officials who visited them.
German prosecutors on Monday said they were investigating the teenager on suspicion of membership in a foreign terrorist organization, alongside the three others.
Read the whole story from Reuters.
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