The raids were linked to an association closed down in 2005
German police have carried out a series of raids targeting homes and cultural associations believed to be used to spread extremist material.
The raids, which took place in several areas, including Bonn and Berlin, were linked to nine suspected Islamists.
The nine men, aged between 25 and 47, are believed to have tried to recruit militants to fight abroad.
A total of 130 police took part in the swoop, confiscating material from 16 premises, including a publishing house.
According to Germany's Deutsche Welle, the searches focused on a community of Muslims in the southern city of Neu-Ulm which has been repeatedly raided in recent years during anti-terrorism investigations.
A cultural association in the city, the Multi-Kultur-Haus, was shut down in 2005 after police said it threatened security in Germany.
A statement from the prosecutor's office said the suspects aimed "to Islamicise and radicalize Muslims and non-Muslims - particularly Germans who have converted to Islam".
It added that the suspects used radical literature, audio and video material, seminars and internet chatrooms to promote their ideas.
None of the men - whom prosecutors believe have been active since 2005 - was arrested, though their homes were among some of the premises searched.