Police in Dusseldorf arrested 40 men of North African origin in a series of weekend raids on cafes, casinos and hookah bars in the western German city.
The 300-strong, six-hour police operation took place late Saturday in a neighbourhood near the main train station, where reports of theft and drug-related activity are frequent.
Police said that they conducted checks on 294 individuals and that 38 of the 40 people in custody were arrested on suspicion of illegal residency.
Six mobile phones connected to crimes were recovered, a police statement said.
The raids, which had been planned since last year, were part of ongoing efforts by a special unit named "Casablanca" to bust a Dusseldorf-based organized crime network.
The raids were not connected to New Year's Eve attacks in the nearby city of Cologne, where men of North African and Arab origin have been blamed for sexual assaults and thefts.