Authorities in Germany have arrested three Syrian nationals in a series of raids conducted in the northern state of Schleswig-Holstein under accusations that they're working for Islamic State (ISIS) rebels in the country.

Federal prosecutors said that the three suspects, aged 17, 18, and 26, were sent to Germany in November last year to "wait for further instructions" on missions they've been asked to carry out. As of now, details on where said attacks are purported to take place remain unclear.

A statement coming from the Federal Prosecutor's office said that "concrete missions or orders have not so far been found in the course of investigations carried out so far." Investigations are currently ongoing, as police have been able to confiscate "extensive material" from the suspects, the BBC reported.

Investigators suspect the three men of having volunteered to do the mission for ISIS, with the 17-year old having received weapons and explosives training from the militants. The suspects were arrested as German police raided refugee shelters in Schleswig-Holstein on Tuesday.

The arrests were made in light of attacks conducted by ISIS agents this summer, which took place in the states of Bavaria and Baden-Wuerttemberg in the span of one week last July. Around 10 people were killed and numerous others were injured in gunshots, bombings, and machete stabbings.