Authorities in Germany detained three alleged supporters of the Islamic State group Tuesday on suspicion of preparing a deadly attack against non-Muslims. Frankfurt prosecutors said some 170 police officers searched three apartments in the nearby city of Offenbach and detained the men, who were already known to authorities. "The intervention occurred in time to prevent a concrete threat," chief prosecutor Nadja Niesen told reporters in Frankfurt. She said that the suspects appeared to have planned an attack in the Rhine-Main region with the intention of killing "as many people, so-called unbelievers, as possible," but it wasn't yet known whether they had chosen a specific target. Niesen said the main suspect, a 24-year-old German citizen with Macedonian roots, had already acquired materials needed to make explosives and searched for firearms online. Police seized various substances and electronic devices at the man's apartment. The other two suspects are Turkish citizens aged 21 and 22. All three suspects are alleged to have spoken of their support for the Islamic State group in the presence of witnesses, who informed authorities, Niesen said.