German police on Tuesday carried out sweeping raids across 10 states in a probe against an Islamist group suspected of propagating hate and inciting 140 youths to fight alongside jihadists in Syria and Iraq.
The group called The True Religion (Die wahre Religion) is now also banned, Interior Minister Thomas de Maiziere said.
"Across the country, militant Islamists came together in this group named The True Religion," he said. "Under the pretext of promoting Islam, under the pretext of supposedly harmless distribution of translated versions of the Koran that took place in pedestrian zones, hate messages were propagated and young people radicalised," added the interior minister.
De Maiziere noted that after participating in the Koran distribution campaign organised by the group, "140 young people travelled to Syria and Iraq where they joined the fight with terrorist groups".
The raids, which targeted around 200 homes and sites in 10 states including North Rhine-Westphalia in the west, Hamburg in the north and Baden-Wuerttemberg in the southwest, began at dawn.
Experts say the German translation of the Koran distributed by the group is a particularly strict version from the original Arabic text.
Tuesday's ban is the biggest such prohibition in Germany targeting Islamist groups after another organisation called "The Caliphate State" was outlawed in 2001.
De Maiziere stressed that Tuesday's action is not targeted against the general distribution of translated Korans, but against those who "abuse religion and who use it as a pretext to spread extremist ideology and to back terrorist organisations".
"The 140 departures by the group's activists speak for themselves," the minister said.
According to figures released in May by intelligence services, 820 militants have left Germany for Syria and Iraq.
Almost a third have returned and 140 were killed while abroad, while around 420 are still in Syria or Iraq.
Germany has so far been spared large-scale militant attacks.
But it was shaken by two assaults claimed by IS group and carried out by asylum seekers -- an axe rampage on a train in Wuerzburg that injured five, and a suicide bombing in Ansbach in which 15 people were hurt.
Police said last month they had foiled an alleged plot by a Syrian refugee to bomb one of Berlin's airports.
Authorities last week also announced the arrest of five men suspected of recruiting fighters for the Islamic State group.