German authorities arrested three people with alleged ties to an Al Qaeda-linked rebel group on Monday in police raids across the country, the federal prosecutor's office said.
Two of the suspects, a German and a Turk, are believed to have travelled to Syria last year and joined the Islamic State of Iraq and the Levant (ISIS), according to Middle East Online, which Berlin - like most Western countries - has proscribed as a terrorist organization.
The third person, a woman, was taken into custody on suspicion of providing 4,800 euros ($6,600) to the group.
More than 100 members of the elite police squad GSG 9, the federal police force and state police conducted simultaneous searches of 10 apartments in Frankfurt, Berlin, and Bonn for suspects ISIS members.
Federal prosecutor Harald Range said that the operation showed "that violent conflicts like the one in Syria have a direct impact on us in Germany".
"We must decisively fight this phenomenon with all the means of the criminal justice system, with an eye to the possible dangers that radicalized people returning from Syria can pose to the population in Germany," he said in a statement.
While Western countries - especially the US and Britain - have backed the rebel forces during the three year conflict, western states have become uneasy over the growing influence of radical Islamist elements among the rebel movement.
Recently, funding for some extremist rebel groups was revoked, and western states have mostly refrained from providing more than "non-lethal assistance" to rebel units; but foreign nationals - including many western citizens - continue to pour into Syria.
Over 75,000 foreign nationals are estimated to be fighting in the Islamic holy war there - including some 660 Germans - and western security services are concerned about what this means for their own countries' future security.
The news surfaces just months after eyewitness accounts confirmed that Islamist groups are training Western nationals in Syria to bring fundamentalist Islam - and terrorism - back home with them.