FRANKFURT (Reuters) - German police detained three people in the western city of Offenbach on Tuesday on suspicion of planning a bomb attack for the Islamic State militant group, prosecutors said.

The three suspects wanted to kill as many “infidels” as possible in the planned attack in the Rhine-Main region, Frankfurt prosecutor Nadja Niesen said.

No specific attack targets were yet known but evidence seized from raids of three homes in Offenbach should shed some light, she added.

German intelligence agencies and police have been on high alert for potential attacks by Islamist militants since a rejected asylum seeker from Tunisia killed 12 people by ramming a truck into a Berlin Christmas market almost three years ago.

The main suspect arrested on Tuesday is a 24-year-old German of Macedonian origin who wanted to manufacture explosives and tried to buy a weapon online. His two suspected accomplices are Turkish nationals aged 22 and 21.

The suspects are believed to have told people they were IS supporters, Niesen said, adding she thought all three were known to police.

Substances that could be used to make explosives and equipment were found at the main suspect’s home, she said. The authorities also secured written documents and electronic data.

Niesen said a decision would be made on Wednesday on whether all three suspects or only one would be brought before the investigating judge at a court in Frankfurt.

The judge will decide whether to issue an arrest warrant and order pre-trial detention.