Berlin's Christmas market truck rampage was the deadly jihadist attack Germany had long feared, as security services have warned of the growth of a shadowy Islamist scene.

Rarely a week has gone by in past years without the arrest of a radical preacher, an extremist backing the Islamic State or other extremist groups with money, arms or propaganda, or of a fighter returning from Syria or Iraq.

Germany's domestic security chief, Hans-Georg Maassen, has likened the rise in IS followers to a dangerous "youth subculture".

He said that while it has drawn some home-grown converts and many female recruits, the main target group has shared the "four Ms" profile -- male, Muslim, with a migrant background and a history of personal misadventure.

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