The charges against the four defendants, all Russian nationals, are serious. Appearing at the Hanseatic Higher Regional Court in Hamburg on Monday, they will be facing accusations of being members of a foreign criminal organization and of supporting a foreign terrorist organization. More specifically, they are alleged to have used social networks to collect donations for the extremist "Islamic State" group(IS), said to be a total of €174,000 ($198,000).

For many years, the danger posed by Islamist extremists in Germany was considered a threat to the country, especially in the period following the September 11. 2001 attacks on the US.

Since then, far-right violence and crime have become a greater threat, according to the authorities. But the risk posed by religious extremists remains high, said Konstantin von Notz of the Green Party faction in the German parliament. Von Notz, an expert on interior policy, is also the chair of the Parliamentary Oversight Panel, which is responsible for monitoring Germany's intelligence agencies.

"Islamist [extremist] acts continue to pose a very serious security threat........

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