Hans-Georg Maassen, the president of the Federal Office for the Protection of the Constitution (BFV), said that the inflow of militants to Syria from Germany is to be stopped, a statement issued on Wednesday.
The domestic intelligence service also expressed concern over the return of those militants to Germany.
There is concrete evidence that some of the German militants orchestrated terrorist attacks in Germany after coming back from Syria, the statement read.
German officials had previously voiced their concern about the issue.
In late April, German Interior Minister Hans-Peter Friedrich confirmed that some German-born gunmen had teamed up with the militants inside Syria.
German security officials have voiced concern over the experience the German militants have gained in Syria and the contacts they have made there.
Syria has been gripped by deadly unrest since 2011. According to reports, the Western powers and their regional allies -- especially Qatar, Saudi Arabia, and Turkey -- are supporting the militants operating inside Syria.
The United Nations says more than 100,000 people have been killed and a total of 7.8 million of others displaced due to the violence.
An estimated 1.8 million of the displaced Syrians are living in neighboring countries, including Iraq, Jordan and Lebanon.
The unrest, which took in terrorist groups from across Europe, the Middle East and North Africa, has transpired as one of the bloodiest conflicts in recent history.
NTJ/BA