A suspected IS recruiter has been arrested during a series of raids in Frankfurt.
The unnamed Tunisian man, 36, is being held on suspicion of supporting a foreign terrorist organisation.
Authorities fear he was in the early stages of orchestrating an attack in Germany with the help of a network of supporters.
Investigators believe the man had been a recruiter and smuggler for IS since August 2015 and according to Turkish officials, he is also suspected of being involved in a deadly museum attack in his homeland in March 2015.
Authorities in Germany raided 54 flats, business premises and mosques across the city and surrounding region as part of a four-month investigation focused on 16 people aged between 16 and 46.
Timeline leading up to arrest:
2003-2013: Tunisian suspect is in Germany
August 2015: returns to Germany as an asylum-seeker
2016: arrested in Frankfurt because he had not finished serving a 2008 sentence for bodily harm
2016: Tunisia is seeking his extradition for alleged involvement in planning and carrying out the March 2015 attacks in his homeland
November 2016: he is released again because he had served his previous sentence and Tunisia had failed to provide full documentation to support his extradition within the required 40-day deadline, prosecutors said
November 2016: he is kept under round-the-clock surveillance
February 2017: the man is arrested in raids planned for four months by German police.