Dozens of radical mosques in Germany are currently being closely watched, Germany's domestic intelligence agency BfV said on Monday.

Around 90 mosque communities in Germany are under surveillance, "predominately Arabic-speaking", BfV President Hans-Georg Maassen said in an interview with German media.

According to the intelligence chief, many of the mosques in question are so-called "backyard mosques" where "self-proclaimed imams, self-proclaimed emirs" rally their followers to deliver "hate-speech" and where they also "incite jihad."

As for reasons behind the targeted surveillance measures, Maassen said the BfV was investigating links to the terrorist group "Islamic State" (IS). He noted that his agency was not monitoring Muslims in Germany while monitoring religious and political extremists.

Maassen also strongly cautioned against "throwing Muslims and religious extremists into the same pot."

"What we need in Germany is a coalition against extremism," he said. "And for that, we need the Muslims in Germany - the moderates - who want to fight against extremism with us on the basis of our constitutional order."