BERLIN—Police across eastern Germany were hunting for a 22-year-old man from Syria on Saturday suspected of planning a terror attack and said they had found “highly explosive” materials in his apartment.

After raiding the man’s apartment Saturday in the city of Chemnitz and failing to find him, police fanned out in a broadening manhunt and detained three people they described as the suspect’s contacts. They published his name—Jaber Albakr—and photographs showing him wearing a dark hooded sweatshirt with a colorful print.

...