German prosecutors say two men who have been under investigation since last year have been arrested on suspicion of membership in the Islamic State group.

Prosecutors said 26-year-old Mustafa C., and 27-year-old Sebastian B., were arrested Thursday morning in raids in the western state of North-Rhine Westphalia. Their last names weren't given in accordance with local privacy laws.

The two Germans are accused of traveling to Syria through Turkey in March and August 2013 where they joined a group known as the Muhajireen Brigade. By the end of 2013, they were suspected of joining IS, undergoing training and providing logistical support during battles.

Sebastian B. returned to Germany in November 2013, while Mustafa C. returned in September 2014.

Prosecutors say there's no evidence they were planning attacks.