Police said Saturday evening's raids on 18 cafes, gambling houses and bars near the main railway station were planned last year and not triggered by the New Year's Eve assaults and thefts in nearby Cologne.
However, those events, blamed on people in a crowd described as primarily of "Arab or North African origin," have drawn attention to crimes committed by North Africans in Germany.
A police statement today said officers checked 294 people, largely men of North African origin, and arrested 40 38 of them on suspicion of illegal residency. They also found six cellphones linked to crimes.