Citing a classified government report, the daily Bild said on Tuesday that the authorities were worried a radicalized individual or small group could target German interests both at home and abroad.
The paper said around 50 members of Germany's militant Islamist scene had travelled to terrorist training camps in 2012 alone. They are thought to have received training from the terror network al-Qaeda on how to plan attacks as "autonomous cells" in Germany.
Another 100 German Islamists are estimated to have already received paramilitary training, and half of that group had returned to Germany, paper said. The classified report said the militants included many German converts to radical Islam.
The authorities' concern about terrorist attacks is growing despite Berlin's refusal to send combat troops to Mali.
Germany has instead increased its logistical support for its French allies in piecemeal fashion. Berlin this week agreed to send a third Transall transport airplane and boost its shipments of equipment to support the French campaign.