Sven Lau was arrested today in the western city of Moenchengladbach, federal prosecutors said in a statement.
Lau is suspected of four counts of supporting the group Jaish al-Muhajireen wal-Ansar, or JAMWA, which was designated a terrorist organisation by the United States last year.
Prosecutors alleged that the 35-year-old was the go-to contact for extremists wanting to fight for JAMWA in Syria and provided financial and material support to the group under the cover of humanitarian aid shipments.
Lau, a convert to Islam, made headlines last year when he attempted to establish a "Sharia police" in the city of Wuppertal to enforce a strict interpretation of Islam.
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"With their propaganda glorifying violence and their alleged help for suffering people in war zones, Salafist preachers such as Lau provide a breeding ground for the radicalization of young men," said Ralf Jaeger, North Rhine-Westphalia's interior minister.
"They are inciting young people to join jihadist terror groups in Syria and Iraq."