"The terrorist organization Islamic State is a threat to public safety in Germany as well," Interior Minister Thomas de Maiziere, estimating that over 400 Germans have joined IS in Iraq and Syria and about 40 have died, was quoted by Reuters.
More than 100 “jihadists” are back in Germany including "some with combat experience who have learned to hate", he said.
"We don't know what they are doing, but it could be that they will carry out attacks," said De Maiziere.
The German move coincides with the launch of a broad US campaign against ISIL in Iraq and Syria, announced on Wednesday by US President Barack Obama.
Joining the campaign, Germany introduced an immediate ban making all ISIL propaganda, symbols and activities.
The ban is not the first against the militant group by the German government.
Earlier in August, Chancellor Angela Merkel has broken with Germany's post-war policy of not sending arms to war zones and has begun to send weapons and equipment to Iraqi Kurds fighting the militants.
Banning the group, Maiziere asserted that security efforts were not enough to stop ISIL, praising the Muslim community leaders for standing up to the "barbaric" organization.
He also urged "parents, siblings, neighbors and friends" to help.
Germany has Europe's second-biggest Muslim population after France, and Islam comes third in Germany after Protestant and Catholic Christianity.
It has between 3.8 and 4.3 million Muslims, making up some 5 percent of the total 82 million population, according to government-commissioned studies.
Militants from the Islamic State in Iraq and the Levant (ISIL) have been widely condemned by Muslims worldwide who staged several protests to express anger against the terrorist group.
Source: On Islam