Germany has launched a crackdown on home-grown jihadists banning all activities in support or on behalf of Islamic State (IS).

Interior Minister Thomas de Maiziere announced a decree outlawing recruiting activities and donations in favour to the extremist group with immediate effect.

The ban also targets collateral activities in support of IS, such as flying its flag, displaying its symbols in public and distributing propaganda material.

Maiziere described IS, (previously known as Isis) as a "terror organisation that poses a threat to public safety in Germany".

The move came after the domestic security agency, released a report on almost 400 German radicals who have joined fighting in Syria, analysing their backgrounds.

The report from the German Federal Office for the Protection of the Constitution revealed that most of the Islamist recruits were young males who failed to finish school and lived at the margins of society, with many being involved in petty crime.

The agency, revealed that only one in four of the 378 jihadists that have travelled to Syria since 2012 finished high school.

Only 6% of the total finished further school training and only 2% went into further education after school.

A large proportion of the jihadists were not just failures in school but also in their careers, the research showed; one fifth of the 378 were registered as unemployed while those who were in work were mainly in low-paid occupations.

Earlier this week, a German extremist with IS identified only as Silvio K., posted videos online threatening attacks against Germany, the Westdeutsche Allgemeine Zeitung newspaper reported.